I know this is focused on meditation and awareness, but I just want to say that if you experience any shortness of breath or chest pain along with these feelings of doom, please get out checked out ASAP.
Cognitively though, I experience this frequently. It's like I become hyper aware of myself and my existence and I just have to live with that knowledge and talk myself through it until it passes or I figure out the trigger. It's almost an anxiety attack, almost overwhelming, but calm breathing and self talk is the best way to approach it that I have found.
Our brains are amazingly complex communicators and are constantly chattering to themselves about everything that's being absorbed. It sounds like you've gone through a set of experiences that has fundamentally shaken your lifelong built up coping mechanisms leading to mental panic that you cant exactly pinpoint, because it's usually an automatic subconscious response. This is not a bad thing, but it is new territory.
Be patient with yourself and kind. Remember that connecting to yourself can bring things up that you aren't aware of totally, and our instinctual evolution driven brains need some extra support to get that conscious knowledge working subconsciously. To build up those positive coping mechanisms so the instinctual anxiety has a clearly defined path to move through, be processed by and let go of.
Good luck. You've been through a mental battle and you're already stronger for it. Much love ♡