I feel , the stress of preparing for the NEET itself would have caused him OCD.
The Internal fear of passing through the exam, is to be handled.
I am sure all your family members and friends would have helped him.
Unless he willing to accept himself regarding whatever the result could be, it is difficult for him to handle this stress.
Next Steps
Do fix an appointment with a Psychologist and help him to share his feelings . That might help him to cool his thought process and make him more relaxed.