Many years ago when I was beginning to experience anxiety (and I had no idea what was happening), I called our doctor's office very late one night when I was having an anxiety attack and didn't know what it was. The nurse asked me lots of questions and had me take my pulse as I counted for her. She asked if I had any Benadryl in the house (I did, for allergies.) and told me to take 2, and to lie down and take deep breaths and call their office in the morning. I suppose the nurse quickly identified anxiety and knew that the Benadryl would act as a calming agent that would let me sleep.
Later on I understood all about panic attacks but that night it was the Benadryl that enabled me to sleep. It's the same ingredient in Dramamine used for travel sickness. It's also used in some sleep-aids since it makes you dowsy.
That's my experience and it was a nurse that told me to use it.