If as some say he would not normally fly like that and there didn't seem to be any power loss, then the factors might be medical.  They need to r/o intoxication, some effect from medication, exposure to a toxin (carbon monoxide, etc.), cardiac issues, and a mental status change due to stroke or mental illness.  Most  partially incapacitated people would have difficulty flying in such a coordinated, deliberate, and extreme maneuvering​ manner, but this appears to be what happened, until the LOC (stall, spin)