sorry if i've asked this before. not sure through the brain fog.
i've had several tachycardia events, and doctors scratching their heads why since i'm hypo/hashi's and on very low dose of levothyroxine.
tested for possible mitral valve prolapse through ultrasound and structurally my heart is normal, which is great news, but leaves us with no other guesses for the ocassional tachycardia.
i was taking toprol, but the side effects are awful, and i'm not yet up to optimum levels for thyroid, so still being slightly hypo, with toprol on top makes me feel like the walking dead. anyone here been on toprol?
my main question though is, has anyone who is hypoT experienced tachycardia events? i would certainly be expecting this sort of thing if i was hyperT, but not hypo.
so now my endo thinks maybe i'm having anxiety attacks. how can i have an anxiety attack while i'm sleeping???? almost every time i get tachycardia its in the middle of the night while i'm asleep.
I too have rapid heart rates and the docs kept telling me that i was having a panic attack, but they were happening in the night too! From what i can gather, and this is after one week in the hospital, my meds were too high, i have lowered them but still experience heart palpatations but not to the measures i had before. Don't let doctors tell u it is all in your head, it's not! Thyroid meds can cause heart palpatations along with other things so keep an eye on it!
I have had the exact same thing for years. If you go back and read my very first thread (I think) I kinda go through everything. But, essentially, it sounds the same. I've only recently been diagnosed with Hashimoto's although I don't know how long I've actually had the antibodies. I've seen a cardio for years now and have gone through taking a beta blocker, the echos, etc. Although my valve doesn't really prolapse, it does flatten some. The cardio thinks I have some mild dysautonomia and does agree that my nervous system is out of whack. I have had panic attacks but sometimes it's just the heart racing, and not panic. I've had both so I can tell the difference. Also, much of the time the heart racing is at night. I still seem to think this has something to do with my autonomic nervous system (which also controls digestion) as my heart occ. also races after eating, or when my stomach is upset. (think I've posted about this before as well).
There's also something called mitral valve prolapse SYNDROME. In the syndrome, you may or may not have MVP, but do have a lot of the other symptoms like palps, heart racing, etc. The problem is a lot of doctors don't recognize the SYNDROME part. There's a lot of info out there from websites, to organized groups and even medical centers dedicated to treating and diagnosing the syndrome. The only really unfortunate part is that there's really no 'cure,' only treatments, one of which you're doing (beta blocker). Maybe you could decrease your Toprol dosage so you don't feel as bad and still get some benefit. I was taking a very low dose when I was on one. Mostly, the treatment is just about really taking could care of yourself.....no alcohol, eating right, taking vitamins, exercising (this is a big one). Anyway, you might check out this option.
I know for many years I've struggled and was looking for something to explain it. When I found out I had thyroid issues, I thought that might be it. I know with Hashimoto's you can swing from hyper to hypo, but not sure how long this can go on for....it's been since about 20 years for me.
hypo AND tachycardia? 
