It depends. If we’re in bed, at night, I’m out within 15 seconds. If we’re in the dungeon, there’s the task of releasing my partner. That pretty much keeps me awake.
To the OP: I’ve got to go with the “it varies” crowd. But even middle-of-the-afternoon sex can produce a really nice nap, so my answer is “it varies a lot.”
Only sex I’ve had is solo, but, unless it is close to bed time, or I just need a nap, it’s enough to make me tired, but not fall asleep. And, since doing it with someone else would require more physical exertion, I can imaging it not helping me sleep at all.
(Didn’t answer the poll since I am a voluntary virgin.)
I have recurring bouts of insomnia; there are some weeks that 2-3 nights a week I’ll still be awake at 3 a.m., and get up for work at around 6. If my wife gets up to pee in the middle of the night and hears me watching TV downstairs, she’ll often come down and tell me to come upstairs so she can… help me get to sleep. It usually works, but sometimes it doesn’t. When it does work, I’m out within minutes of disengaging. When it doesn’t work, I lay there another 20 minutes or so, then go back downstairs and read or watch TV.