I've been living in a state of existential terror for nearly a year now and I can relate to what you're saying.
"Now, here's the difficult to explain bit. I have this constant awareness that I'm inside my own head and that trapped feeling too. It is so much worse when I'm alone which is also scary as I'll soon be living alone again after just buying a house. It's so hard to explain but it's like I can't believe my own consciousness, or I freak out that I am seeing through my eyes or something. I feel like an alien trapped in my own body, it's bizarre and terrifying and I don't mind admitting that it's led to suicidal thoughts in the past and those have come creeping back to. I know it comes and goes and it's just another form of anxiety and obsessive thought but its so difficult."
I've suffered this along with a whole range of uncomfortable symptoms. It's a very hard thing to explain so I understand but the feeling of being trapped for me lingered a long, long time and led, in past, to desperation and suicidal ideas. Does it feel to you like every moment is one of uncomfortable clarity? like I'm never in the flow or doing things on autopilot. I will say I'm a lot more calm with it nowadays, and when I have that moment it is more easily brushed aside but it is not gone. Valium, Mirtazapine helped me deal with the worst of the physical feelings in the head.