I've also found that there are no measures that work against it so far. Massive exercise does not work, reading boring stuff does not work, relaxing hot showers don't work. Getting drunk and stoned enough to fall asleep typically defeats itself by making me stay up long enough to get enough alcohol/THC in my system. I tried taping my math teacher's voice, because it always put me to sleep in class, but that turned out to be a regular occurrence due to not getting enough sleep in the first place. Melatonin stopped working after two weeks. Post-coital drowsiness has yet to be tried, if you'll excuse my vulgarity there, and it is my last hope. This has been going on for as long as I can remember, and until my dad and sister told me how quickly they fell asleep, I thought it was a normal thing. Then, because it was dinner, I winged a bun at their heads.