THE PILOT EXECUTED A LEFT (SOUTH) CROSSWIND DEPARTURE TOWARDS HIGHER TERRAIN AFTER DEPARTING RUNWAY 27; THE PLT WAS FOLLOWING A SLOWER SINGLE ENGINE AIRPLANE THAT HAD PRECEDED HIS DEPARTURE. GROUND WITNESSES REPORTED THAT AS THE AIRPLANE APPROACHED THE HIGHER TERRAIN IT ENTERED INTO A LEFT BANKING TURN. DURING THE TURN THE AIRPLANE'S WINGS OSCILLATED RAPIDLY. THE AIRPLANE STALLED AND CRASHED INTO THE CENTER DIVIDER OF CALIF STATE HWY 395 WHICH IS ADJACENT TO & PARALLELS THE EAST/WEST RUNWAY. THE POST ACCIDENT AIRPLANE/ENGINE EXAMINATION DISCLOSED NO EVIDENCE OF ANY PREEXISTING MALFUNCTIONS OR FAILURES. THE AIRPLANE HAD EXCEEDED ITS MAX GROSS T.O. WEIGHT AND IT WAS NEAR ITS AFT CENTER OF GRAVITY LIMITS. THE PLT HAD COMPLAINED TO HIS DR. ABOUT EPISODES OF FORGETFULNESS AND CONFUSION. THE DR. RECOMMENDED THAT THE PILOT CEASE ANY FLYING ACTIVITIES UNTIL HIS MEDICAL CONDITION WAS DIAGNOSED AND TREATED. THE PLT DID NOT HEED THE DRS. ADVICE.