What just happened?!?!

Hey ladies and gents, what do you even do when a guys you’ve been dating for 6 months just drops off our of no where. The last conversation we had was on Saturday night to where he just never responded back and now it’s been four days I haven’t heard a word. Everything seemed fine idk what happened.

Any advice would help. Should I reach out or just not even bother at this point? Thank you!