In all seriousness, it might have been a small clot passing through arteries in your brain. I've known 3 aneurism victims in my life. Two of them lived through it. But sadly one of them was a 48 year old hopelessly addicted alcoholic who was a 24 hour maintenance drinker. She was the one who's brother found her dead on the floor of her home. Autopsy showed aneurism.
Tell your Doctor about things like that!
The Bible speaks a lot about knocking. Maybe it was God trying to get your attention....
LOL! Alcoholism does a lot of things to a person, but knocking on the head is not one of them, it just barges in and takes over. It may knock you out!
Not sure this forum can help you , Sebby.
Maybe you were dreaming. If it was a knock on your head and you are not sleeping next to someone, then it may be a question for the "Weird or What " site!!!
Not making light of it, but It does have me scratching my head!
Good luck in getting answers
CML