A big giant yes.
Exertion intolerance is a huge deal for me. Huge. Sometimes it takes a while (like up to 48 hours) to hit me and sometimes it's right away (like someone unplugged my power cord). It can happen after prolonged low-grade activity or after a short burst of exertion. Mental stress can do it (like from an emergency) but physical stress seems to be the most deleterious.
I often don't have any symptoms at all unless I try to do stuff. You ask if people get worse from energy expenditure, but I'd go so far as to say I sometimes only get bad at all from energy expenditure!
When I've been pushing for a while (days or weeks), then the crash is more dramatic - brain fog, panic, intestinal distress, no appetite, POTS, headache, dizzy.... Like my body just holds up a massive stop sign. It's tough to know how much energy I have in my reserves, so sometimes the crash is a surprise. I'll often muse that I was feeling okay (or close enough) and didn't know I was pushing until it was too late.
You mention normal levels of energy expenditure, but I have not gotten close to normal energy expenditure since I got sick with Lyme. (And the thought of working out is laughable! Exercise for me is a walk around the grocery store or working in my yard. Months go by that I'm not even capable of those things. I marvel at people who go running ... on purpose ... and survive!) It's one of my most disabling symptoms. I "pay for" energy usage afterward. When I'm in an okay stretch health-wise, I can use more energy without paying for it, but I usually don't know right away when I've reached my limit, so it's important for me to stop exertion before I'm feeling the effects.
Things I could do pre-Lyme: any Jillian Michaels workout video, stay up all night and function the next day, clean the whole house at one time, bike across Boston at rush hour faster than anyone else, walk miles hauling a full week's groceries without minding, carry my child seemingly indefinitely.
Things I can't do most of the time I've been sick: go up the stairs more then twice per day, vacuum more than one room, walk one block, dance to one song, sing a full song, climb a ladder, stand up for more than three minutes. (There have been months I've been unable to do any of these things and have needed to be helped to the bathroom and supervised while I bathe. So things vary!)
Right now I'm doing better than I have in years, overall, and here's the maximum of my physical capacity: walk around the block, go fruit picking (if someone else carries what I pick), play croquet, do yard work (but not mow the lawn), vacuum one floor of the house, cook a simple dish, dance to two full songs. I'm downright thrilled about
these things.
I do identify as having CFS/ME. It's often caused by an infection, which can include Lyme. Like so many things, the diagnosis of CFS/ME is just a shorthand descript
ion of a collection of symptoms, with no assertion about
cause. I have (or have had) all of the symptoms. Friends with CFS/ME who don't identify as having Lyme experience all the same things as folks on this forum do. Their treatment, symptoms, and health trajectories are exactly the same aside from antibacterial treatments.
As for the mechanism involved, it always seems adrenal to me, and inflammatory. Maybe you're right about
mitochondrial involvement, though. I should look into mitochondrial health more concertedly.
Your actual question was whether it's common. I don't know, really. I don't have fatigue in the sense that I am sleepy more than regular people. I'm awake all day, just can't do much. I see people here talk about
how they are so bummed because they can't lift as much weight at the gym since they got Lyme, and I marvel! Exertion intolerance is very disabling, so I can see how it makes you feel concerned.