What Causes Hair Loss While On Bystolic?

I had a few vasvagel episodes in the past. I was first pic on attenlol 25 mg. Then 50 mg. Was on that for approx 10 yrs. I am also on thyroid meds daily and also 2 yrs ago was put on bystolic 5 mg. I myself started cutting the pill in half because my thyroid had been up and down. And my hair is falling out a lot. I did at one point stop the bystolic totally And my dr. Wanted me to start it again ,so I could then take a stress test . But I was not able to run for the test so iam now waiting to see my dr, in feb. But since I ve been on bystolic again I’ve lost more then 50 percent of my hair ,I don’t know if it s a thyroid problem or the beta blockers causing this problem...