Different anon, I had a similar kind of imaginary friend to the poster with The General imaginary friend.
Mine was named Penny, and my mother told me that I used to do really out of character things and tell her that Penny told me to do it. I was a really well-behaved and anxious child. I guess I would do something wild like break a glass or one time I believe my mother caught me eating a cake out of the fridge that was meant for a get-together that evening. Really weird stuff that was abnormal for me.
I do remember Penny a bit, but only in flashes- he was a little creature of some sort. More like a tiny person, coppery, I think that is where the name came from. It is not at all vivid of a memory, but I do get flashes of recognition, and a distant voice/whisper kind of thing. Apparently, during the time I was "friends" with Penny, my mom said I had instances of sleepwalking that had never occurred before nor since. She recalls one particularly creepy night when she woke to me sitting on the edge of her bed and watching her sleep. When she opened her eyes, she saw me and asked if I was okay. I asked her, "Momma, what do people look like?" And then I laid on the floor and fell asleep. She was freaked out, to say the least. I remember waking up on the floor.
I've never had any auditory or visual hallucinations, or any sleep disorders. Nothing like this ever happened again.