An angel, cast from grace, and left to watch the people he had all too evidently come to care about suffer? How could he not have PTSD? And some major abandonment issues for good measure.
In fact, it seemed to Lester that they were dealing with a full-blown identity crisis.
Up until very recently, he'd thought that possessions were the province of ghosts and demons. But then, angels were spirits too, so it wasn't that much of a stretch to conclude that they must need some means of interacting with the mortal realm. Perhaps. He tried not to jump to too many conclusions.
"We're going to do everything we can for Sam," he promised, "But only ready to accept our help." How many shrinks does it take to change a lightbulb? Just one--but the lightbulb has to want to change.