Worked in a grocery store during HS and uni. Always was friendly with customers, but at times (especially the elderly) would chew your ear off.
Now I understand they just wanted human contact and conversation but my stoned teenage brain did not.
One chap sticks out in my mind.....I was loading up the grape display and bloke comes over and starts off "Can't enjoy grapes anymore since my wife died a few years ago....."
We all have those days. Good on you for recognising when you feel like that.