Okay, welcome to the forum and I've read your posting and concerns.

Sinus tachycardia in of itself is not a concern in the absence of other supporting clinical data. It's important to realize that transition to a sedentary lifestyle, whether healthy otherwise, can produce dramatic changes in heart rate on even mild exertion.

Anxiety can certainly cause a general increase in basal heart rate and moreover, fears about one's health can drive it even higher. You need to stop trying to diagnose yourself or otherwise raise concerns about POTS and dysautonomia. These conditions demonstrate very characteristic signs and the tendency by laypersons to practice clinical diagnosis by merely matching and associating symptoms which seem similar is entirely subjective and inaccurate.

You should also realize that sympathetic tone, which is responsible for increasing heart rate, responds to feedback from the sensory network and vigilance to one's heart rate will invariably produce an increase in rate, sometimes remarkably depending upon the reaction of the individual to unexpected values.

You need to relax. The tests described would have elicited markers for any type of underlying cause and negative test results literally means negative and not any type of approximation or uncertainty.

You'll be fine. Have a Happy New Year.

Best regards,

Rutheford Rane, MD (ret.)