Hi, welcome to the forum, this seems to be independent of Benadryl. From your history it suggests that you are having Sleep-disordered breathing. It is important to rule out type of sleep apnea like Obstructive apnea, Central apnea and mixed apnea. You need to undergo tests to rule out the type of apnea.
Few of the tests include Apnea index, Apnea-hypopnea index, Respiratory disturbance index, Desaturation and Arousal index.
If the tests are suggestive of sleep apnea the treatment in the form of supplemental oxygen and drugs like acetazolamide and theophylline against prescription are promising. Benadryl is known to be associated with sedation. You may try discontinuing Benadryl after consultation.
I suggest you to consult physician for further evaluation and treatment accordingly. Take care and regards.
You should discus this with your docotr because issues people have with a medicine need to be reported no matter how long the drug has been on the market. There could have been a bad batch from that manufacturing plant. You may also be having an allergic reaction to it. Only your doctor could tell you that.
Several thoughts.
Benadryl is a first generation antihistamine. There are much better ones on the market these days and you should try one of them. I really like Zyrtec (brand or generic).
Second, you may need a sleep study for your breathing issues while sleeping. You might have apnea which can be very dangerous.
Feel better and praying for you to find answers.