
Elizabeth P. answered 09/05/19
Patient math/stats tutor with Ph.D. in Psychology
The water hitting that spot acted as a retrieval cue, helping you to access that memory from your long-term storage. Just like songs can remind us of certain people or smells can remind us of certain places, sensations can act the same way. The warm water hitting that one spot on your head reminded you of when you busted your head. It may be that the warm water felt similar to blood flowing from the spot, which reminded your brain of the accident in the past.
(Now I am reminded of when I was approximately 6 years old and fell backwards and hit my head on a brick fireplace and needed a couple stitches in my head!)