I believe that I understand your predicament. The best time to tell him the truth is while he is still in the hospital. The hospital is a safe place. If, after hearing the news, he becomes manic, the hospital staff can treat his symptoms accordingly.
You should also immediately inform his treating doctors and caseworkers. They need to be consulted so they can prepare for his possible negative reaction. It might also change how they plan for his discharge. He may need a different place to live or additional resources, and that information would likely be important for them to know before they release him from the hospital.
If you were to wait until he returns from the hospital, and he reacts negatively and becomes manic, the risk for violence increases. Your life may be in danger, and so might the lives of his mother, other family members and your pets.
I hope that my response reaches you in time to be of assistance and that you’re able to remain safe. If you feel that your safety is in danger, do not hesitate to contact the authorities. Do what is necessary to protect yourself. Please take care.
Dr. Kristina Randle