There is a similar symptom that is due to depression that feels like one is in limbo or detached. The common intense thought depression is different. I experience this lack of awareness depression 30 plus years ago. My psychiatrist explained it as cognitive fatigue from overload. As he described it, the brain gets clogged with toxins from a emotional or physical stress and just stops functioning.

Has your psych considered anything like a depression due to finishing school ? Sort of a post partum depression ? My brother suffered a depression episode when he finished an intense year long project at work. The adrenaline from the pursuit of the project became his existence. When that adrenaline trigger was ended, he collapsed. People, especially men, often experience this when they retire. It can be a malaise or worse.

Google Post College Depression or Post Graduation Depression. Both terms are used.

It would be worth trying to find something to do that creates a routine.

The defense industry deals with this same issue as Top Secret programs get finished and security clearance employees need to sit in the freezer for days and weeks ( a room with just books and magazines ) so their clearance level is maintained until the next program starts. The stress of going to work to do nothing is problematic.

You could try a 5-HTP supplement. The serotonin that 5-HTP provides helps with some depersonalization issues.