You're not alone. A lot of people have pretty hellish start-up effects on N-acetyl-cysteine or glutathione. For me, it mostly involved muscle weakness, air hunger, insomnia, and delayed constipation followed by diarrhea. Other symptoms included brain fog, night sweats, and aches.
I generally start at a low dose, and only raise the dose slowly. ("start low and go slow")
I started with a single 500mg dose of N-acetyl-cysteine on a Monday. That was all I took for the first week.
By the following Monday, the effects from the first dose wore off, so I took another 500mg dose, and then another dose on that Friday. So I took 2 doses in the second week.
The third week I took three doses, on Monday, Wednesday, and Friday. The fourth week I took four doses, etc.
By the 8th week, I was taking 500mg N-acetyl-cysteine every day.
But this was a pretty hellish eight weeks, and I didn't start to feel the positive effects of the increased glutathione until week 12.
After week 12, though, I had a clear improvement in most of my symptoms. In fact, boosting my glutathione is one of the greatest long-lasting improvements I have had, reducing all of my core ME symptoms noticeably.
Hope this answers your questions.