Much of it is down to sleep deprivation, not getting a proper sleep because at the time you should be in a deep sleep we’re at bloody work. If you’re on nights then if you’re one of those who is trying to have a normal sleep pattern on a weekend it can cause all kinds of problems.
As for the handbrake I’d not say it was so much forgetfulness as paranoia and I doubt you’re alone in giving it a double check.