What causes irregular breathing and drowsiness ?

Lots of things: There are so many possible processes which could cause either of those symptoms or both related to the same clause that you will have to give us a little more information in order to be helpful. For instance, is this problem sudden in onset or has it been developing? Have you had it for a long time at the same intensity level? Are you a smoker or do you have asthma? Are you anemic?