Is this exercise intolerance?

Tl;dr: walking that raises my heart rate makes my lips go numb and makes me nauseous and dizzy. Is this common?

The long version: I’ve heard the term, but I’ve never been sure what exercise intolerance is. Now, 3 years into my diagnosis, my head pain is finally at a level where I can start exercising regularly. I can’t bend down at all because I get dizzy/instant headache and PT, so no gym for me. Instead, I’ve just been walking. But when my heart rate gets even a little bit elevated, my lips and lower face go numb, I feel like I’m going to vomit, and I have to stop and sit down before I pass out. After a few minutes, I can get going again and manage 30-40 minutes at a slow-to-regular pace. Is this what people mean by exercise intolerance? And is there anything I can do about it?

I’ve been on topiramate for the past year. Was previously on acetazolamide, which was so horrendous I lost loads of weight just by not wanting to eat. My BMI is now 30, so I need to lose more weight, but I’m in my 50s and my body doesn’t seem to want to let go of any more fat with sensible eating alone.

Any thoughts or experience?