Bradycardia at rest, Tachycardia when standing

[jdraper]

Looking back, I realize that I have posted questions here before, and 10 years later I am still having similar issues.

I'm 37/M , and when I'm relaxed either sitting or lying in bed, my heart rate drops uncomfortably low - sometimes in the low 40s.  When this happens, I am short of breath and have chest discomfort - especially if I try to take a deep breath.

When I stand up, I feel extremely light headed for several seconds, and then my heart rate will usually jump to over 100 bpm.  Once I sit down again, it will usually settle at around 55-60 until I am very relaxed again, at which point it may or may not fall back into a low rate.  I have these problems most days, but sometimes I feel the symptoms worse than others.

I've had a battery of tests recently - treadmill stress test, echocardiogram, multiple EKGs, 48 hour holter, and my cardiologist says that my heart is great and I don't have to come back and see him for a year.

I have also been having episodes of tachycardia that come out of nowhere - it even happened during my echo (I was lying there and my heart rate jumped up to over 135 out of the blue - it freaked out the tech and she stopped the echo for a few minutes and tried to call one of the Drs into the room.  After about 10 minutes, it dropped down to around 100 and she was able to finish the test).

I am in horrible physical condition - on my treadmill test, I was *barely* able to finish the 6 minutes of walking at the first level of incline.  The cardiologist says it's physical deconditioning, my primary doctor says it's anxiety, and no one has any solutions for me.

I'm wondering if it could be thyroid related - I've had seevral blood tests that showed normal TSH but low T4, and my dr was going to put me on medicine for that but my most recent test showed that my T4 was back to normal.  I do have a family history of thyroid problems (1 sister had hasimotos, 1 had graves) but my Dr doesn't seem to be even slightly concerned with that now that I had a normal test, and he says that he doesn't feel like I need to see an endocrinologist.

I'm really at a loss, and I know that no one here is very likely to have an answer for me, but thought I'd try anyway hoping that someone that has had or is having similar problems might see my post. :)

[jdraper]

Forgot to add - my blood pressure is also all over the place.  About half the time it's between 115/65 and 125/80 and other it can be anywhere from 135/80 to as high as 165/90 at times.  I've been in the ER with chest pains and it's been 185/100,but by the time I was discharged, was back down to 110/70.

Just another crazy thing that none of my docs can explain but nor does any of them seem to be even slightly concerned about.