If you are having difficulty in my class, talk to me!
I try hard to be sympathetic to the difficulties students in my classes have, both academic and otherwise. Don't wait until the day before the exam to let me know you're having trouble! But even in the middle of an exam, if you suddenly forget everything you know, tell me! I may be able to talk you through it, or find some other suitable way to deal with it.
However, the one thing I will not tolerate is cheating in any form. You should realize that even the suspicion of cheating makes it difficult to obtain strong letters of recommendation -- and this is far more important to your long term career goals than the grade you earn in my class.
My policy on cheating is that all suspected cheating will be reported to the appropriate office, usually the Dean of your College. Provable cases of cheating will also result in a score of 0 on the assignment in question, and may lead to a grade of F in the class.