Hypnagogic hallucinations
How it feels:
When a person is on the verge of sleeping but still awake, he sees weird pictures before his eyes. Often these are scary faces and fantastic creatures.
Why it happens:
This is one of a few types of hallucination that mentally healthy people may have. Children have them more often (source), which could be the reason they don’t want to go to sleep. Such hallucinations may be due to stress or simply a good imagination. They can also appear if you go to bed drunk.