to my children when they were little, I explained it thusly:
"Mommy has HOLES in her head, where stuff gets lost, or flies away."
and: "Mommy's brain is like an Etch-a-Sketch right now, so tell me that all over again, please?"
to compadres, explaining vertigo, I'd say: "It's like being commode-huggin' DRUNK, but without the FUN singing-dancing-happy part first! Just go straight to the sickening SPIN-DIZZY part, where you holler 'STOP the WORLD, I wanna get OFF!'"
about exhaustion, I'd tell my brother it's like how HE feels after finishing a marathon, but I only have to walk for two blocks to get that tired...
to my sister, I'd say: it's like a week-long 50-mile backpacking trip through the Emigrant Wilderness, carrying 60 lbs... but the pack doesn't get any LIGHTER as you use up stuff in your pack, it gets heavier and heavier, and your knees start to buckle, and your ankles start to collapse, and the pack belt burns and pinches (the MS hug-squeeze).