Achenbach syndrome

Not sure how clear the picture is. I have something called Achenbach syndrome, it is harmless, but sometimes one of my fingers will quite rapidly appear very bruised on the inside, with no apparent cause, the first time it happened I was baffled, how could I have possibly bruised my finger so badly in my sleep and felt nothing?! It doesn’t occur often and the bruises disappear very quickly, they are usually completely gone within 3 or 4 days.