Ed used to pee on things when he wasn't happy.
Usually stuff on the floor (you couldn't undress and leave the clothes on the floor!!).
It was a general nervous / stress / display of not being happy thing with him. If you moved stuff around he peed, if you cleaned the litter tray peed (anywhere but the tray), if hub and me had an argument he peed, if it was bonfire night he peed.... you get the gist - nothing was physically wrong - it was purely psychological - he just hated anything to change in the slightest.
Hope your behaviourist can help, and as others say, try to stay calm, so he doesn't pick up on your worry.