Medical stumper

I am at my wits end with a medical situation with a pt so I thought I would throw it out to the group here for some advice.

I have a pt in a mental health facility who I have a confusing situation with. This is a overweight woman mid 40's with no serious medical history. Doesn't drink or smoke, hx of depression, meds consist of ativan PRN, ambien, and celebrex.

The pt wakes up fine, and then every afternoon around 1-2pm the pt feels out of it. She describes it as a pressured head, exhaustion, sometimes heart races, and just over all malaise.
BS are always stable unless there is a episode of accelerated HR, BS are WNL.

Dr's think pt is just "acting out" for attention but I honestly think there is something more going on here. Even if the pt is engaged in an activity that she is totally engrossed in and loves I can see it come over her from a distance and she struggles to get through the activity. A lot of times she won't tell anyone and it will go undocumented unless a staff member questions her as to if she is "ok".

Can anyone think of what would be the cause of a afternoon transient issue like this? I am just stumped with this one.

Thanks,
Zenny