Hi @Roses86 I hope you're feeling a bit better this morning. It sounds like this may have happened for the first time? I have PTSD related nightmares regularly, and when they first started I felt completely out of control, my heart was pounding, I felt like I was going to have a heart attack, I was sweating, I wanted to throw up...all the fun things. Now when this happens, what makes things a little bit easier is to turn on the light straight away, focus on senses, what can I see in my room etc and also reminding myself I am safe now and repeating that. Sometimes getting up and moving to another location like the kitchen and making a cup of tea and watching the kettle boil is helpful. Sometimes a cold shower is helpful.
There is also a DBT skills chapter on Nightmare Protocols which I have found helpful (BUT only for non-PTSD/flashback related nightmares - if it's for that, recalling the nightmare in detail has had a detrimental effect). I think if you Google it, you should be able to find a free copy and see if that's relevant for you, 'DBT nightmare protocol PDF' looks like it does the trick for more info.