Quite simply, you're never entirely "off" when you own your own business. I went to a funeral yesterday and was mostly OOO but still had a couple of "sorry, what do I do with this?" emails. (Which is entirely fine, by the way). I then woke up at 5 today and first thing I did was go through my email. The worry never really leaves you.
HOWEVER, what I will say, is that putting the right structure in to avoid being available all the time, or being constantly on call really helps. I turn everything off at 5 and unless there's something they need me for, my team deals with the rest (we're open til 11). Switching off those notifications is vital to me.