The left front of my neck is bruised.why?
Hard to tell..
sadly with this little information you are probably not going to get much of a satisfying answer. Usually when there is abnormal bruising it is all over your body, rather in one specific spot, so this is less likely to be part of an overall illness.
Usually when there is a single unexpected bruise in 1 area you accidentally hit it or fell a sleep with an ill fitting shirt collar