This large amount of work can be exhausting and make your playing difficult as you need to play high ,soft and exposed passages on tired chops. If it happens over a long period of time, it can cause you to gradually lose self confidence and to be more nervous in general.
In my previous orchestra, I was often put in a situation where I had to perform delicate passages at the end of very tiring rehearsals which was causing me stress that compounded over the years to the point that I started shaking a bit when I had to play by myself. I also had trouble sleeping at night and wasn't feeling well both physically and mentally.
One day, after yet another crappy night of not-so much-sleep, I've decided to just take it easy in the rehearsal. We were playing Shostakovitch 8. I thought I would just play everything sort of "mezzo-something" to relax. So I stopped trying to blow the roof up in fortissimo passages and I didn't try to be almost inaudible in pianissimos anymore. And then something happened: after about 30 minutes of this, I began to feel really good! My heart beat felt normal again and my entire mind and body was relaxed and comfortable. Like a ton of pressure was suddenly off my shoulders. Ironically, as I felt better, my tone was instantly better and I could play louder and softer since I wasn't wasting all my energy on every line and wasn't pushing myself to the edge all the time.
It makes sense: if your body is comfortable, your mind will be comfortable and your confidence level will increase.
I asked the conductor in the break if we were making enough sound. He said it was just perfect like that.
So I asked myself how many times in a concert do we need to play our loudest or softest volume? Not very often actually. In fact, we can play within our comfort zone more than 95% of the time. We still need to have the ability to play extremely loud or soft in case we need it but most of the time, it's not necessary. Even if it's pianissimo, the part still needs to be heard or else, the composer wouldn't have written it! And if it's fortissimo, well. you're not alone in the orchestra and it might not be the most important thing going on. You have to use your artistic judgement.
The past two weeks reminded me of this as I got so tired after playing so much loud stuff in Alpine that I had a hard time in the Beethoven the week after and was a bit discouraged. I remembered what I did a couple of years ago and took it easy from the third day of rehearsal. Things went much better after that and the concert went great!
There is a time to give 110% and there is a time to take it easy. You can save yourself a lot of stress by pacing yourself properly depending on how much you have to play in a particular week and by using your artistic judgement to determine your dynamics. You'll feel much better and will have a much better time playing in general.