Has an one had an experience like this. After been to a therapist he went home feeling fine but later he had this sense of dome come over him next day it was a bit like anxiety attack which slowly got better over the following days . He said it was not like a normal panic attack . I had something the same mine came on for no reason just a depression just creeps in and hits you and the panic slowly goes away ,
I know for me that sometimes after going to Therapy,even though I felt better the underlying cause of my panic/anxiety was still there.So I would still have anxiety attacks but not as hard and scary like panic attacks and they could last all day or for a couple days and just slowly get better.I also discovered over the years that the depression just keeps creeping in whenever it likes,even if things are going good so I just learned to recognize when that’s happening and try to get up immediately and fight it.I fight it by exercising real quick even if its just for a few minutes,going outside for a walk(if the weather permits)eating something healthy like an apple or having a warm beverage that has no caffeine in it.I have never been able to fully understand why the panic/anxiety attacks still come and mess with me but as time passes I have gotten better at coming up with ways to fight them and make them weaker.I hope my comments help.Take good care!