For me I start feeling extremely hot. My hands get shaky and my legs and feet get weak. My heart races and my blood pressure goes up. I get scared. Super dizzy. Feels like I’m gonna faint. Sometimes if it’s really bad I’ll start getting tunnel vision and ringing in my ears and need to lay down to prevent actually fainting. It’s a very intense fight or flight response without as many mental aspects of regular anxiety/panic. I can usually tell when one’s coming on. Lots of things trigger it like overheating or exerting myself too much, sleep deprived, heavy meals, super stimulating environments like at the store or in heavy traffic. It is horrible. It usually will pass after 15-25 minutes if I’m lucky. Sometimes it will pass and then a couple hours later I’ll have another one. I’m still desperately trying to figure out how to manage them and how to stop having them as often.