I think you should trust your instincts- if you feel this stress is a problem then you should confront it and not ignore it in attempt to study more. I have the same issue, I struggle with anxiety and try to ignore it but I find it doesn't help me at all. I can't stand it when friends/family/other people tell me "just don't think about it" or "you're worrying too much." This works for some situations, but I think most stress is not going to just go away on its own.
I have no idea what the source is of the stress, but you said you were really stressed this semester in particular? If your learning/studying is being affected I assume some of it has to do with your courses? Maybe they're harder this semester?
The obvious advice is that if you have concerns about your courses you should talk to your profs or TAs. That has helped me in the past- even if all I do is ask them to look at it a test/assignments and for their feedback on how I can improve next time. Mac has an academic skills page here:
http://csd.mcmaster.ca/academic/onlineresources.html . I find it helps me to review some of those sometimes on essay writing, studying, time management, etc. I think it's normal for a lot of students to not understand the expectations of the university or their courses, and that can add to a lot more stress. People panic over what's going to be on a test, how they're going to do on an assignments, but as long as you understand HOW you should study for the class and HOW you're going to be marked in the class you shouldn't need to stress too much about it. It helps to look for patterns in your classes, how they test you, how they mark assignments, etc.
If your stress isn't really academic related, then I would still say to find some way to figure out what exactly is stressing you out and how to deal with it. I find my perfectionist tendencies(in uni, and everything in general) stress me out so I'm trying to change that.... but then I beat myself up because I feel like I'm failing at not being a perfectionist! haha, obviously that's really backwards and not accomplishing anything. So obviously worrying about it TOO much won't help. Honestly I think some of the expectations of uni are a little unrealistic, there really isn't much you can do to control stress in university.