A different perspective might be able to clear things up and clear your understanding of what he is going through so that your concern for him is one of compassion and not fear - if that is the case, I really don't know.
"he lost contact with reality from time to time."
"What can be done to make his journey back to life shorter and less unpleasant?"
"Then being in a mental hospital is lacking in reminders of the real world."
This shows in my perspective how mixed up we are with the mind. A suggestion is that he is now finding the REAL LIFE on a deeper level, probably increasing his brilliant understanding of the universe. Here in our "daily life" our minds trick us into believing we are living a real life, although we are actually not. We are universal beings and when you get a stroke of "mental illness" you are just shifting perspective, becoming more true, going into REALITY, out of this illusion - the world of the mind. It can be very scary for the being (actually still the mind being scared) but most of all it is scary for those minds who are around that person. They will try their best to drug him or her back to the illusion of the mind. If it is the case that he is stuck in the astral world experiencing a lot of emotional turmoil medication might very well help him to cope for a while until he is through that friction.
It is hard to suggest anything since he is not explaining himself what he is going through. If I was his friend, I would just spend time in his presence and be there with him. BE - in presence, being true, being real - not in mind trying to understand. Just follow the flow of energies and IT will know exactly what to do to get him more capable of living both in reality as a BEING and function as a manifested body in this illusionary world of existence.