I have them too... Usualy take 2-3 days to go away.
Maybe you can try running with the train instead of against it. this sometimes helps because after a while you will be thinking the same things over and over again and you can find a pattern and thus dismiss it as being fake.
One thing that helps me is sleep much sleep. And believe it is hard to fall alsleep when having a panic attac.
The only thing that actually makes is worse is alcohol...
Keep it up yr on the right path.