I have had a similar problem. I’m just dropping off to sleep and I get a fluttering in my chest and I wake up gasping. It was a panic attack in my case and it started when my mum died in 2014. It’s almost stopped now (but I still have an anxiety related sleep problem that means I can’t fall asleep most nights:-(). So how did I get rid of the panic? I first became very afraid to go to sleep, then I tried some relaxation breathing before bed and in time it went away. To be honest, it went away when I stopped being afraid of the sensations. Sorry I can’t be more helpful.