Catalina shut down

Thanks for suggestion.  I never try anything when I don’t know what I’m doing.  Which is almost everything.  Went to Apple Chat and I really don’t know what happened, but worked o.k. for a couple of days, then same thing.  Then remembered what store said when I bought my new iMac/Catalina, 4 months ago - “never shut down.”  Then re-read an article on subject.  I just have an old habit to “shut down”.  My last iMac was 8-years old.  Always “shut down.”  Also, old habit of if it’s not in use, “shut down.”  I think also, some apps don’t completely shut down, so the the computer doesn’t “shut down” and after time just “restarts” itself.  Ah yes, sometimes quickly, sometimes slowly. 

Thanks for suggestion.  I never try anything when I don’t know what I’m doing.  Which is almost everything.  Went to Apple Chat and I really don’t know what happened, but worked o.k. for a couple of days, then same thing.  Then remembered what store said when I bought my new iMac/Catalina, 4 months ago - “never shut down.”  Then re-read an article on subject.  I just have an old habit to “shut down”.  My last iMac was 8-years old.  Always “shut down.”  Also, old habit of if it’s not in use, “shut down.”  I think also, some apps don’t completely shut down, so the the computer doesn’t “shut down” and after time just “restarts” itself.  Ah yes, sometimes quickly, sometimes slowly. 

Seems like I'm a constant novice on Macs. I only use my iMac several hours during the day. Usually nothing after 6:00 p.m. until 8:00 a.m. the next day. Shutting down when not using it is just an old habit. My previous iMac was 8-years old (OSX 10.11 - ElCapitan.) So, I'm many years behind the curve. Then, you think it would be o.k. to SLEEP during the day when not using & then SHUT DOWN over night?