my mac goes to sleep mode unexpectedly and unwantedly while working in it

Check the "Hot Corners" in System Preferences->Mission Control.

This looks like you may have set one hot corner to put your mac to sleep. If that is the case, it is very easy to activate by accident.

Perhaps this information from Apple may provide insights to this issue

links below

Set sleep and wake settings for your Mac - Apple Support (CA)

Change Displays preferences on Mac - Apple Support (CA)