Advice for working on your feet?

Anyone who works a job where they’re constantly walking and standing please help. I’m a server and lately feel like I’ve been fighting passing out my whole shift and it’s really impacting my work. My hands shake like crazy, heart racing, I lose my vision like I’m ab to blackout at times, legs feel heavy, etc. I think I’m one wrong move from being fired and constantly get yelled at by management for not keeping up and using the bathroom (literally just to cool off and sit down for a sec). I think the main issues are the hours and the heat. It’s always extremely hot inside and heat intolerance is one of my worst symptoms and I will be basically drenched in sweat (gross). I also work breakfast which means I’m sleeping less and not eating much before work (also bad for me). I worked nights and it would be hard at times but not like this. I’m also in a bad flare right now because I also have vestibular neuritis from a cold I got in December. I’m looking for a new job to do nights again because I can’t afford to take the pay cut to work a desk job. I guess this is kinda a rant too but just hate feeling like I can’t keep up and my coworkers hate me lol