It’s rare, but it’s happened to me on occasion. Sometimes, after a dive I will experience a
horrific migraine, followed by unbelievable sleepiness. The urge is so strong – I once fell asleep on a pier with
my BC still on. After about five minutes sleep, I feel perfect. I’ve always suspected a CO2 buildup due to
overexertion, but never was really sure as to the cause. If you’ve ever experienced anything like this,
this discussion on CO2 buildup will
probably be interesting for you.