I think it is exactly that, coming to grips with your own mortality and overanalyzing it. It is my problem as well. I have gone through spells in my life to where when someone would make plans for us in the future, I would outwardly acknowledge the plans, but inwardly not believe I would be alive.
That sense of being disconnected, I totally know what your are talking about. I get that a lot while driving, but it happens in social situations as well.
I try to explain it to people that can't understand, as sort of like, putting on a cheap halloween mask (with the rubber band which holds it on your head) and pulling it about 2 inches from your face, and trying to view the world from that perspective. It's like your peripheral is dark, you have no feeling in your face and the your consciousness feels like it's on the verge of blinking out like turning off a television.
When this happens, I just have to get away, or pull over, collect my thoughts, call someone, play guitar, whatever I can possibly do which is comfortable to me, and will help put something else in my mind other than what is currently wreaking havoc.
Losing 2 people in your life is a major deal, and one that's hard for anyone to be stoic about.
I remember a lot of my anxiety kicked into overdrive after 9/11. Then in 2005, after years of battling cancer, I watched my mother quickly fade in a hospital bed, medicated on morphine. The same exact day she died, my friend took his own life. I had to leave my mother's funeral and go directly to his.
These feelings don't always hit suddenly, but it's the anxiety and stress of them that build as your emotions are trying their best to get a handle on the situation, and people like us (I would assume maybe you are an introvert too by nature?) tend to internalize - even to the point of picking up others emotions and feeling their anxiety, or even thinking you are the cause of someone else's bad vibes.
I'm new to this forum, but have met others with the same type of mental process as we have, and one thing I've noticed is we all seem to be very empathic .
You're not dying from this, you're grieving, and these panic issues are the way your brain chemistry deals with the process. I think your best option is to talk to people, go to a therapist, get something prescribed - a short, fast acting benzo - these steps will help with the crippling situations. And unless you suffer of clinical depression, these steps will help - and if you do have clinical depression, seeing a therapist is the first action to take to try to help you through it. As hard as it is to believe in times like this, there are people who really, really do care.