HELP! ATENOLOL

Hello. I'm 22 years old and I suffer from anxiety (which causes me to have rapid heart rate) and high blood pressure. I've been on Atenolol for the past year and it has worked GREAT to control both anxiety and high blood pressure. My medication is 25 MG but I only take half of it which is all I need. But my problem is, at night, when I have 1 or 2 erections and then go to sleep, my heart hate is slow and when I fall asleep i seem to have shortness of breath and wake up all of the sudden gasping for breath really bad. This happens for around 1 or 2 hours or so and it's stressing me out really bad and I don't want to develop heart disease if this continues. During the day I feel perfectly fine but after I have erections and go to sleep this happens and I'm only 22 years old! I wanna point out that this has started since taking atenolol and only after I go to sleep. I don't know what to do or what to change.

note: I take half of a 25 mg tablet a day.

Thank you very much, I hope I get some answers and suggestions. I will be seeing my doctor around November.