What do you do after a bad range session?

Just forget about it.  I have had many bad range sessions and the next day my swing was back to nomal.  Not a believer in biorhythms, but some days you have it, others you don't.  Best thing for me is to not dwell on the bad session and start fresh the next day.

Unless you go back out there, there's nothing you can do except suck it up and give it your best tomorrow. Plus, it sounds like you were working on somewhat of a swing change, so don't worry about it too much. If you have time before your round, go to the range and hit some 2/3 punch 7i's.

Forget it. I sometimes have terrible sessions because I was not focused on a target out in the range and was hung up on swing fundamentals. Once you are on a course and you have a target and a goal your body and mind should get back to normal, whatever that is for you. Just slow it down, find a good tempo and have fun. The rest is gravy.

First of all, I'll stop it early. About one out of 10 times, I just chunk the ball with all different clubs. I realize it's not my day, and go do something else. No use reinforcing frustration.

Have a beer and move on.  You arent going to have your best game every day and you cant let a bad range session get to you.

I do one of two things, first one would be stop when it does not get better and forget all about it. The other thing I do is just keep hitting shots until I find what I am looking for. Rarely will I not figure out what is going bad. I have played this game going on 50 years and if I can't figure out what I am doing wrong after an hour or so I just quit at that point and come back the next day and try again. A few times I have gone out on the course and just played nine holes not trying to d anything but just hit the ball and go get it and hit it again. This is good therapy as well it keeps you out of the trend of thinking about doing something and just hitting the ball.

Certainly true that even if you're hitting terrible shots you can at least still be making progress.  But I think the OP is talking about that dreadful feeling you get when you're hitting shots much worse than you usually do and you worry that it's going to happen the next time you're on the course.  This would apply mainly to those of us that don't work at golf centers and/or can't get to the range as often as we need to between rounds.  So - we know that even though it's Weds, the next time we're going to touch a club is on the tee box Saturday morning.