If you describe someone as a worrier, you mean that they spend a lot of time thinking about problems that they have or unpleasant things that might happen.
worrier in British English
(ˈwʌrɪə)
noun
a person who often worries about things
Are you a worrier, prone to fretting about the smallest of problems?
He's a real worrier.
Examples of 'worrier' in a sentence
worrier
He was a do-er, not a worrier, one of those people whose instinct is for action without hesitation.