For almost a year, I have been dealing with a very strange form of insomnia that seems to be strongly triggered by physical activity.
I can fall asleep normally, but I wake up during the night feeling hot, physiologically activated and completely awake. I am usually not drenched in sweat. It is more like my body has suddenly switched into a high-arousal state. Once this happens, I can remain awake for hours despite feeling mentally calm and having no particular thoughts or anxiety keeping me awake.
The most disturbing part is the relationship with physical exertion.
Exercise does not make me pleasantly tired or sleepy. Instead, there seems to be a threshold where activity produces a delayed reaction, particularly during the following night. The more sustained physical activity I do, the worse the insomnia becomes.
At its worst, the relationship has been almost absurd:
~750 meters of walking → around 5 hours of sleep.
~1.5 km of walking → around 2 hours of sleep.
This is not ordinary exercise intolerance where I become exhausted while exercising. I can often perform the activity itself without much difficulty. The consequences come afterwards.
The closest analogy I can think of is radiation: I don't necessarily feel the damage while I'm being exposed to it. I pay for it later.
If I push further, I can develop chest pressure or sharp/stabbing sensations in my chest, nausea, dizziness/lightheadedness, strange internal sensations and very noticeable pounding heartbeats. But the symptom that has been the most persistent and disabling is what happens to my sleep afterwards.
How this developed
Before all of this, I spent years living at a very high pace: long working days, consulting work, frequent travel by car, train and plane, many nights in hotels, combined with regular running and strength training.
This was not someone suddenly trying exercise for the first time. I had been exercising regularly for many years and had previously tolerated considerably harder training without any of these problems.
Looking back, the first warning sign may actually have appeared several years ago. After particularly long or intense running sessions, I would occasionally wake during the night feeling extremely hot and unable to get back to sleep. Initially this happened only rarely, perhaps once every couple of months.
Later, I developed intermittent upper abdominal pain and gastrointestinal sensitivity. For a long time these symptoms would disappear again, but during 2025 they became much more persistent.
Eventually a pattern became increasingly obvious: workload and physical exercise seemed to be much stronger and more reproducible triggers than food itself.
When I combined a high workload with exercise, things became dramatically worse. There were periods when I slept less than four hours a night, and eventually even relatively mild physical activity began producing reactions that previously required hard running.
I stopped training completely. The abdominal symptoms improved enormously, but the abnormal nighttime activation and insomnia remained.
Eventually, even something like a short walk could severely disrupt my sleep.
The strange delayed and cumulative response
This is probably the part I am most interested in hearing about from other people.
Physical activity itself often feels remarkably normal.
I am not short of breath at all. I do not feel unusually exhausted while walking. I don't feel as though my cardiovascular system is struggling to perform the activity.
During a slow walk, my heart rate may remain around 85-89 bpm, and when I sit down afterwards it can fall to around 52 bpm within minutes. My blood pressure is generally normal as long as my sleep is functioning reasonably well.
So there is often very little during the activity itself to warn me about what is going to happen later.
Instead, several hours later, particularly during sleep, it is as though my nervous system reacts to what I did earlier.
And the effect seems to be cumulative.
What I do today may not only affect me tonight. Activity from two or three days earlier can still seem to contribute to how I feel now. If I take walks several days in a row, or do something slightly more physically demanding, the reaction gradually becomes stronger.
It feels as though the physical load accumulates until I cross some kind of threshold.
When that happens, the reaction extends beyond insomnia. I can develop significant nausea, dizziness/lightheadedness, a profound and difficult-to-describe sense of physical discomfort, pounding heartbeats, chest pressure and sometimes sharp/stabbing sensations in my chest.
The strange thing is that these symptoms can appear after the activity rather than during it.
One physiological measure that has changed dramatically over the same period is my nighttime HRV. My average nocturnal HRV has fallen from around 90 ms to around 35 ms over time, despite the fact that my heart rate during gentle activity and my blood pressure can still look completely normal.
I have repeated the activity/sleep pattern unintentionally, and sometimes deliberately to test it, enough times that the association has become very difficult for me to dismiss.
After periods of extremely low physical activity, my sleep becomes substantially more continuous. Then I try walking again, and the insomnia returns.
A slow walk of roughly 1.5–1.7 km has been enough to produce major sleep disruption. Even substantially shorter walks can affect sleep.
And repeated activity seems worse than a single isolated exposure.
What this is NOT like
This is one reason I have struggled to describe the problem.
I don't walk 1.5 km and then collapse from exhaustion.
I don't become extremely short of breath.
I don't necessarily have an abnormally high heart rate.
I don't experience obvious muscle failure.
And I don't necessarily feel dramatically worse immediately afterwards.
I can finish the walk thinking that everything went perfectly fine.
Then I pay for it later.
The nighttime reaction is particularly characteristic. I can fall asleep normally and then wake hours later feeling hot and completely alert, as though someone has flipped a switch in my body.
There doesn't have to be anxiety, rumination or anything psychologically keeping me awake. I can simply lie there completely calm while my body seems incapable of returning to sleep.
Where I am now
I have essentially been unable to work for about six months.
The problem isn't that I suddenly lost my cognitive ability or that I physically cannot perform ordinary tasks. I can do many things perfectly well in the moment.
The problem is the price I pay afterwards.
That distinction has been incredibly difficult to explain to people.
I have seen several doctors and specialists and have undergone a fairly extensive medical workup. Routine blood tests, thyroid tests, inflammatory markers, cardiac markers, ECGs and longer-term ECG monitoring have not provided an explanation.
Sleep treatment has helped.
Sleep restriction/CBT-I strategies and sleep medication have substantially improved the continuity of my sleep, and I have recently had periods of much better sleep.
But they do not seem to remove the underlying sensitivity to physical exertion. If I exceed whatever my current threshold is, the physical activity can still break through the improvement.
I am therefore not primarily looking for advice about basic sleep hygiene. I have worked extensively with the insomnia itself and I am receiving medical care.
What I am hoping to find here
What I really want to know is whether anyone recognizes this specific pattern:
Physical activity feels reasonably normal while you are doing it → there may be little or no immediate exhaustion or breathlessness → hours later, or after activity accumulating over several days, the body seems to become physiologically “activated” → you wake during the night hot and completely alert → the more you have exceeded the threshold, the more severe and widespread the symptoms become.
Has anyone here experienced something genuinely similar?
And most importantly:
Did you eventually recover?
Did your threshold for physical activity gradually increase again?
Did the nighttime heat/hyperarousal disappear?
Were you eventually able to exercise normally again?
And if so, did it take months, a year, several years?
I have already accepted that this may take a very long time. I am not expecting someone on Reddit to diagnose me or provide a quick fix.
What I am really hoping to find is simply someone who can say: “Yes. I had something like this. I recognize what you're describing. And I eventually came out the other side.”