This is absolutely a function of the sympathetic nervous system being activated and dominant as opposed to parasympathetic dominance.
Whenever you get tired, dehydrated, annoyed, keyed up for whatever reason (that "easily irritated" feeling, when you're tired, you know how everything gets 10x more annoying?) thats sympathetic nervous system activation. It's essentially your body going into potential war mode, survival, fight or run. The sympathetic nervous system doesn't know that its being activated due to a bear in front of you or because you're tired, it just gets activated. You ever get in a near car crash, sitting perfectly still, and afterwards you're breathing hard, even though you never moved from your seat or exerted yourself? Sympathetic nervous system.
When that system gets activated, it keeps your heart beating hard longer than necessary, keeps you primed and wanting to move around. Thats also why like in the fight videos or police bodycams, when people start to get "activated" you can see them become visibly more animated, unable to sit still, looking around a ton (hypervigilance), and flip out over dumb shit - their sympathetic nervous system is going crazy.
You're probably fine, I'd probably grab an EKG or 2 off your watch just to make sure things are cool, and I'd probably go do a sprint or something outside and see how your heart rate recovery is today to see if it was a temporary problem.
