Partial freeze of system

I'm running 10.13.1 and I seem to be getting a partial freeze. I can sliest a window and move it around, but the program never shows as selected on the top bar. I can not enter anything with the keyboard, but I can move from say safari, to mail to activity monitor. I can not select a particular app in activity monitor, but I can change from cpu, to memory ... The system eventually unfroze after it went to sleep and then I was able to enter in my password again and the freeze was gone. Any ideas? This is very aggravating.