Is it normal to be so tired after a meal (mainly breakfast)?

That's because according to your other post you are waking her up too early instead of letting her sleep until SHE wakes up.
You have to quit trying to get mom on your schedule, and let her be on her own schedule. Your life will be SO much easier if you do.

Your mother is 96 with dementia. Let her go back to sleep after breakfast and rest as long as she'd like.

My Husband would fall asleep right after any meal, sometimes during it.
He had Alzheimer's as well as Vascular dementia and the more he declined the more he slept.
It does take energy to digest a meal so falling asleep would be one way the body directs energy to digestion and lets the rest of the body rest.

I think at 96 with dementia sleeping a lot is normal .

My husband with dementia and heart issues (he recently passed at 71), would get up, get dressed, go to his chair in the living room, and fall right back to sleep. I let him sleep as much as he wanted.

Yes, normal to be tired after any meal for anyone, and things are exacerbated in the elderly.

My husband sleeps after every meal. He is 85, and was diagnosed with dementia 8 years ago.

At 96, she can be tired. With later stages of dementia, she can be tired. Seems like you should let her get more sleep.

Jenjcronin: Unfortunately her dementia is the key here.