Hypnogogic / Hypnopompic Hallucinations

Last night, I was laying in bed and heard a distinct five loud knocks on the upstairs wall. Thinking the neighbors were miffed at us, I got up and looked around to see if it might happen again but it didn't. I asked my kids if they'd heard anything and they said no. When I say I heard them, they were clear as day, yes-they-happened woke-me-up hallucinations.

Turns out these are called hypnogogic hallucinations and happen when you are falling asleep. Why they were so vivid, I don't know, but they can involve the hearing, sight taste and a few other senses. Sometimes, I even feel like someone is violently shaking my bed!

This is a good explanation of the two common types of hallucinations that happen while going to sleep or while waking up.