Yeah its adrenalin you're tapping into. Because you are run right down (which is why you are tired and fatigued) you are running on your "reserves" of energy to get things done, when these reserves get really low then the body helps us out by releasing a bit of adrenalin to "keep us going".
The "benefit" is we get an energy kick and can go a bit further
The downside is we can if we are not careful it becomes habitual to live in this way - running off adrenalin to get us through a hectic day etc., which is fine until we encounter some outside stressors or worries, which demand us to push ourselves even further, which then drags us even deeper into our reserves and nearer our limits.
Now it is touch and go whether or not whether or not we start malfunctioning, which if we do shows up as symptoms, which easily triggers anxiety (because we are already releasing adrenalin), which we are already depleted of, which triggers panic attacks, which triggers more worry, which triggers more symptoms, etc., etc. etc., etc. and before we know it we are stuck in full blown anxiety.
So I wouldn't advise you live in this state for long - not now you can SEE it anyway - as it is a sign that you are near the edge and my bet is you've lived in this state for years and just not known it.
In the past when you felt like this you will have just used this extra energy to squeeze something else in - another hour at work, a gym session, another task, etc. and simply just not known how close you were to "burnout", but now you have tipped over the edge and have had a scare, you are "watching" yourself like a hawk and SEEING this thing for the very first time - which is shining some light on the process and very likely showing you where you have been going wrong all these years.
Now I may be way off - but I really don't think so - as that is exactly how it all happened to me
Hope it helps