How do you know ur having a panic/anxiety attack

Cuz what if something’s actually wrong with my heart or breathing ? And it’s not a panic attack? I feel like I’m just working myself up and making it worse. It’s hard to sleep cuz it’s always when I’m ab to go to bed that this happens with my heart rate spiking or going really low. I’ve gone to the doctor n they said I was fine. Anxiety medicine only sometimes helps. I’ve always had anxiety but its only bad every few years. I’ve had it under control this last year but then last week this feeling started happening at night whether it be before I go to bed or legit wake me up from bed. I’m not stressed ab anything to the point it would make me feel like this. I’ve been through much more stress and nothing like this happened. This isn’t my usual anxiety symptoms. Super confused.