It means committed to a mental hospital. E.g. in Massachusetts the relevant law is in Section 12 of the chapter, so to "section 12" someone or just "section" them is to commit them to a hospital against their will.

Presumably he meant he can't go to a cryonics org or a regular hospital and just ask to be cryopreserved, because that would be suicidal, and voicing suicidalality would get him sectioned to a psych hospital.