it's a thing that they call yoga nidra, yoga nidra actually means yoga sleep, and it's a sort of meditation that you listen to, there are number of scripts, I've talked about this on podcasts before but I'm going to post a link to the two that I like most, that allows you to consciously bring your entire body and mind into a state of deep relaxation, and sometimes you fall asleep and sometimes you don't, this is done for 10 to 30 or even 60 minutes at a time.