Basically, if you don't like it, don't fly. There could have been all sorts of reasons - haze causing overload, fatigue that you weren't quite aware of, etc. But trust your intuition. I once left a fly-in early, and flew back to my home airfield as fast as possible, nervous as anything and not knowing why. Five minutes after I got back, an absolutely humongous and unforecast thunderstorm hit the area. I mentioned how I'd been feeling, and a zillions-of-hours instructor/ examiner told me to develop that kind of intuition, and always trust it when flying.
Now, if it keeps happening for no reason, that's a different matter. You can develop phobias about flying, or flying solo, at any time - I did, for no apparent reason, after a few hundred hours.
If that's the case, talk to an instructor, push yourself but not so hard you scare hourself more, but it really will have to be get-back-on-the-horse time.
But as a one-off, don't worry. I'm sure there was a reason. It's just that your conscious mind doesn't know what it is.