Feeling Like the World is Ending related to panic attacks?

[Confusedpanic]

So ever since getting my vitamin D level back up to normal (and taking xanax and zoloft) my panic attacks have decreased dramatically, where I only experience them once or twice a week and usually upon waking up. As of recently though, I've been having mental disturbances where I will out of the blue get the feeling like the world is ending. There is no racey heart feeling, tingling, dizzyness (though I have felt a little dizzy with headache with them) or typical other sings of panic attacks, I just mentally feel like the world is coming to and end, this is especially triggered more often when hearing a loud noise (which I presume I think is the loud noise to signal the end).

I just wanted to know what this could be exactly :( It's worrying. I would sometimes wake up in this state, but today I just started feeling like this tonight and its been going on for about an hour (with no loud odd noise trigger), where I just "feel" like impending doom is coming (<-- that of which I know can be a sign of panic attacks) though in general still this feels more completely mental and less of me having a physical reaction. It bothers me to the point where I feel like crying because of how irrational these thoughts are.

I'm hoping this is nothing to worry about heavily and (thankfully) it doesn't happen all the time, and might just be correlated with panic attacks, even if I'm not having them. I really don't want this to be something serious as I have been doing so well lately with taking care of myself and managing my panic attacks (which I think I was genetically preconditioned to)

Any insight would be great.