Phillip I would get checked out by an endocrinologist if your cortisol levels were raised this might indicate something going on in your endocrine system.
Since your test results were "normal" I would not worry too much. However, a heart rate that high for many hours is definitely not a good thing to put up for any length of time. It can wear the heart out faster. Maybe you should get a second opinion, wouldn't hurt.
Hope you feel better and your heart slows down, I know how tiring it can be.
Oh I forgot to mention that the it was sinus tachycardia each time.
I did have my thyroid checked. Once it showed that I was hyperthyroid but the other two times it was normal. The T3 and T4 were checked as well as the TSH. The one thing they did find though is that my cortisol levels were above the normal range, although nobody seems concerned about it.
The fact that your echo and ekg are normal is a good thing. That means your heart is structurally fine and you haven't suffered any heart attacks. That said, was your heart rate elevated when you had the ekg or holter and were the results reviewed by a cardiologist? If so, if I were you, I would go see your GP and have your thyroid checked. So first, see a cardiologist if you haven't yet, then go see your GP. I might even go see a pulminary doctor to have your lungs checked to make sure it isn't something with the lungs causing your heart to speed up due to lack of oxygen. The thing to note is the ER's sole purpose is to treat the immediate symptoms and keep you alive, hense the term emergency room. It may be better for you to go to a doctor who will investigate what is going on. If you have trouble with one then go for a second opinion with a different docotor, shortness of breath and turning blue aren't things you want to let slide. I am not a doctor and so I can't really say if turning blue is of any detriment but from what I have learned with my own svt condition, your heart rate being elevated is not something that will likely hurt your in the long run, especially any rates that don't much exceed 150. Ones over 200 start to get a little troubling but there are people in permanant afib who live long lives with a fast heart rate. Obviously you will want to get to the bottom of why but just to easy your mind a bit it is probably unlikely you will succumb to sudden cardiac death but just go and make some appointments to get to the bottom of what is going on. Take care, I do hope you feel better soon.
Depending on the type of tachycardia it is, it may not necessarily be life-threatening, but it still would be debilitating and extremely uncomfortable, and not necessarily safe, either. If your hands are outright turning blue, that is a sign that they're not getting enough oxygen.
I notice that your pulse increases a lot when you stand up. This tends to be a sign of dysautonomia, which just basically means your autonomic nervous system isn't quite working as it should. When it's not working properly, it may do things like speed your heart up too much and try to over-compensate for standing up, which does sound similar to what you're going through. There are many types of dysautonomia. One of them is Postural-Orthostatic Tachycardia Syndrome, commonly abbreviated as POTS. People with POTS have a very large increase in their pulse when they stand up. You would need to find a cardiologist that would check you for that and other types of dysautonomia. Best of luck.