TL;DR: I have exercise-induced insomnia for which no one has been able to explain or provide a solution.
I used to exercise regularly. I would wake up every weekday at 6am, bike to the gym, and exercise for about an hour before work. I would usually jog or do some other cardio for 20-30 minutes, then do weight training for the rest of the hour. I had help from a personal trainer, so I knew what I was doing.
I felt great, and I was in the best shape of my life. I kept this up for about 3 years, before something strange happened: I would wake up around 2 or 3am, unable to fall back asleep. I was 33 at the time, and I know sleep patterns can begin to change around this age.
At first, I noticed that I slept much deeper on days I didn't exercise (e.g. weekends). Then I began waking up in the middle of the night, but would usually go right back to sleep. It got worse. Eventually, I would wake about 4 hours after falling asleep with a feeling like an intense adrenaline rush or panic. It would last about an hour, and I would have poor, restless sleep the rest of the night.
I did not have trouble falling asleep. I was in bed at 9:30pm every night, then would read a bit with lights out by 10pm. I would fall asleep within 10 minutes.
When this started happening, I adjusted my routine. I worked out during lunch, or in the evening. No change.
I tried doing more or less cardio vs weight training. No change.
Today, if I exercise at any point during the day, I will only get four hours of good quality sleep.
I've been to several doctors, sleep specialists, and neurologists. I've had multiple take home sleep studies, as well as one on-site at a medical institution. The only thing they've been able to confirm is that I do indeed wake after 4 hours if I have exercised, but no one can tell me why. Many doctors don't even believe my story -- they think it must be psychological stress that I insist on tying to a physical cause.
I have found that walking, low-intensity biking, and hiking are all acceptable forms of exercise that do not trigger my insomnia. I can hike 10 miles and be fine. But if the hike is over very steep terrain, or if I were to jog for 10 minutes, then I have insomnia. So the intensity is definitely a factor.
The sleep studies did reveal that I have very mild sleep apnea. My doctors have told me that normally it would not warrant treatment, but it could be related. However, the usual recommendation for such a mild form is simlply "get more exercise".
My current pet theory is this: following a day of excerise, one's muscles will repair themselves during sleep, usually around 3 or 4 hours into the night. This process requires oxygen from the blood, so if my sleep apnea lowers my blood oxygen levels, then the repair process might cause it to dip below some threshold; my body panics, sending adrenaline through my body to wake me up to address whatever is happening. However, my sleep studies showed my blood oxygenation stayed over 90% the entire night.
I'm currently trying out a CPAP treatment. I'm still adjusting to it, but so far it hasn't made any difference. There's no real reason to think that it will, but I'm willing to try anything at this point.
When I tell this story, most doctors look at me like I have three heads, so I thought I would seek the collective wisdom of the Internet.
Cheers!