We all have days once in a while where our chops just don't respond like they should. This can be caused by various factors: sudden change in temperature or humidity, general fatigue, over-practicing the day before, lack of practicing, illness, stress before a performance etc...
If you are generally in good shape and your chops normally work fine, you probably should just take it easy for the day without trying to force to play louder in the high range. Forcing your chops when they don't feel well is like scratching a skin rash to make it feel better. It really doesn't help and you'll just get more anxious about it.
Do what you have to do for that day with the chops that you have and put the instrument back in the case. Go do something else if you can and forget about it. Your chops should feel better the next day if you give them a chance.
If you are a bit stiff a few days before a performance, take some time to play slow and easy pieces that you won't play in that performance. It'll relax your embouchure and undo some of the stiffness.
As for over or under practicing, it's up to you to determine how much you really need to practice to achieve your goals and keep a strong embouchure. You can talk about it with your teacher. Stick to your plan but be flexible about it when needed.
If your chops don't go back to normal after a few days. You might want to take a few steps back and play everything softer and slower for a couple of days or take an entire day off to relax your face.
You can also try to be a bit less perfectionist. If you don't allow yourself any mistakes, you'll tend to get a bit stiff which will affect your chops.
In any case, you need to be patient with your body. It has ups and down. There are different solutions for different situations. Most of the time, things go back to normal by themselves if you give yourself a chance.
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.