Hi Lilu,
Too often with anxiety disorders, so much is happening in our minds that is very hard to control, at the times it happens, it is not something you can automatically turn off like a light switch.
When you do talk to him during these episodes, how are you handling the conversation?
We often fear especially when the anxiety rises, that our spouses, boyfriends, girlfriends, will not understand that it is not as simple as saying "Just dont think about it", that by far is the worst, as it just happens, and then we the anxiety sufferers worry that we will lose our partners because they don't understand the anxiety disorder, and would rather chuck it all for someone who didnt have it.
Probably the source of his anxiety is this, fear that you might not understand and leave him, so his automatic thoughts with his anxiety would be those of that nature, you and previous relationships, or seeking and actually seeing a whole scenario of you with someone.
My advice is to just listen and give reassurance that you will understand the anxiety, and sometimes just extra special time with him, and letting him know he means everything to you, after time will phase out of the feelings of abandonment, then the anxiety will decrease, as will the dreams then, and the thoughts.
Trish