I hovered on my name and it had written on it:-
-5 user was removed.
Can anyone explain what happened? thanks.
I tried to see the name.
You weren't removed. What it means is that a user who had previously up-voted you has been removed. When a user gets removed, all the reputation they have given out is cancelled; from looking at your profile, it seems that someone up-voted one of your questions (giving you 5 points) and then their account was deleted.