Roommate with anxiety. is suddenly scared of meds, complains of different pains, and is inverting socially. what could it be?

Several possible : Your roommate could have some type of anxiety disorder, a depressive illness, or psychotic illness. Or other problem too. S/he needs an urgent evaluation by her general physician regarding the pain, but also probably a psychiatrist to further explore the anxiety & whatever else might be accompanying it. Please encourage your roommate to seek help for these concerns.

Depression / Anxiety: Your roommate sounds as though he or she may be depressed. I would suggest that you do what you can to encourage him or her to see a therapist or doctor.