My previous employer had an area specifically for that. Headquarters of a large retail company had a nurse's station for employees who felt ill or had a headache. Off of that area was a darkened room with a half dozen or more LazyBoy recliners for employees to rest or nap in. Everything was above board, manager was notified. We were told "if you need to take a nap, then go take a nap" . I did so occasionally it was not considered to be a bad thing at all.
My current employer doesn't see things that way. I drink at least a pot of coffee every day myself to stay alert at work. Then I have trouble sleeping at night sometimes.