It seems to happen to others. Kind of "getting out of bed on the wrong side" sort of thing.. Maybe it's a mental thing or physical.. I find that it still happens to me.. It's not going to slow you down much.. I look through guitar videos, study up a bit on theory, listen to my fav rock station.. Skip practice and do my chore.. Maybe just jump on to a different lessons... mass around with the scale or chord tools to see if I can apply what I've learn from earlier lessons..
If you have electric and acoustic guitars switch out and try the opposite one.. Some times just a few minutes rest and try again..
I hope I hit on a few solutions to get you going..