Need reassurance please or at least advice.

Hello. Need advice on how to react or not react to a work colleague who is a known bully loud, we were winding each other at work last wk back and forth childish yes. But it was getting or would get heated i didn’t want to back down or didn’t. Can tell he was getting annoyed also me also. Thursday i was on a high. Then Friday until today i have been ruminating over and over what’s going to happen at work on Tuesday when we see each other again, i don’t want to react but i don’t like bully’s. So i,m scared of how or what happens. Incase my job is on the line as he very close to the owner. Union rep also. Do i just smile and ignore and stay calm i really would Luke advice to settle down my obsessing of what ifs. Thanks