Dealing with Intrusive Thoughts at Work

does anyone else get really intrusive thoughts that stop them from being able to do things that are in front of them? i was at work today and i started thinking about what if my sister died i would be so lost and i was thinking about everything that would happen afterwards and i started getting really upset like i wanted to cry and and i couldn't focus, i had to be told multiple times to focus on what i was doing and i was trying but i couldn't stop thinking about it. my sister said if i cared i would focus but it isn't like that because i do care, but the thought was in my brain and i couldn't get it out. does anyone have any advice as to how to deal with this? other than just "deal with it later"