I get the muscle fatigue after activity as well as the too exhausted to move thingy with or without activity. I've had the latter come up on me while out walking or while doing other things like washing dishes, cooking, bathing etc. I just have to stop then and find somewhere to sit or lay down.

I've walked 15 minutes from my truck when exercising my dog and then spent 3 times as long getting back to it. Then have had to sit in my truck for up to half an hour before I can drive or have to call someone to come and drive me home. That sort of fatigue seems to be more common for me when it is warm out, so I'm pretty careful in the summer months about going very far from home or my vehicle.
Of course, my dog thinks those days are just awesome because he gets to sniff about, play with sticks, and thoroughly enjoys himself while I sit and rest .

On top of that, I now also have what seems to be more of a brain/neurological fatigue. It causes a type of narcolepsy (unexpected falling asleep), if I sit still for a few moments.
It isn't always there, but when it is, I can have over 10 attacks in a day. When it hits, my mind gets sort of stunned, what ever may be in my hand drops to the floor, and either that wakes me up or I catch myself mid doze-off as my head bobs forward. It isn't fun to wake up as I'm about to face plant into a bowl of soup or onto the keyboard of my computer. .

When I talk to my neuro or PCP, I avoid using the word fatigue and describe what I am experiencing instead; and do so in terms of how the muscles become weak after activity, excessive sleepiness, extreme bouts of general weakness or sudden loss of consciousness etc.
That usually prompts them to ask more questions, rather than them assuming that they know what I mean.

Hope that this helps.

With love, Erika