With apologies to my fellow English speakers on the Eastern side of the Atlantic, I just have to relate this piece of research:

A recent survey of 10,000 English men revealed that 48 percent actually fall asleep during sex.

The amazing part is that particular factoid is only part of a larger musing on the age-old question of why men fall asleep after sex.

It turns out that sex releases high levels of prolactin, a hormone which induces weariness when injected.

Even better news for you insomniacs out there, masturbation only releases 25% as much prolactin as intercourse, so you now have a scientific basis for requesting sex from your partner. You can thank me later.