is it okay for an 18 year old boy to cry?

Recently I have been really stressed out because of struggles with my exams. I come from a very academic family (both parents are doctors and I have really smart siblings). I like to think I am smart too but I have a problem with dyslexia and it has always has had a negative effect on my education and as a result I don't do as well in exams. This really gets to me and I sometimes have been crying hysterically whenever i'm alone, but when i'm in front of my family I just pretend I am fine. I really try hard but it doesn't ever seem to pay off that much. :(. I would be very grateful if you could give me an answer to my problems.