THE PLT MADE A FLT OF ABOUT 30 MIN TO PRACTICE LANDINGS, THEN LANDED TO PICK UP 2 PASSENGERS. ABOUT 10 MIN AFTER TAKING OFF ON THE 2ND FLT, HE BEGAN HAVING SYMPTOMS OF A MEDICAL PROBLEM. HE SAID HE FELT HOT & THE AIR FELT STAGNANT & STALE. THE VENTS & A WINDOW WERE OPENED & HE BEGAN RETURNING TO THE ARPT. HE ATTEMPTED TO TUNE THE RADIO, BUT COULD NOT FIND THE FREQ. SEVERAL TIMES, HE BLACKED OUT & REGAINED CONSCIOUSNESS. A SHORT TIME BEFORE THE ACCIDENT, A WITNESS SAW THE ACFT FLYING VERY LOW. HE STATED THAT THE PLT WAS 'WORKING THE THROTTLE & DIPPING THE PLANE' BUT REPORTED THE ENG RAN SMOOTH AT HI & LOW POWER. SUBSEQUENTLY, THE ACFT COLLIDED WITH TREES & CRASHED. ALL 3 OCCUPANTS WERE TRANSPORTED TO A HOSPITAL. THE PLT'S MEDICAL PROBLEM WAS DIAGNOSED AS VASOVAGAL SYNCOPE. REPORTEDLY, SIMILAR EPISODES BEGAN WHEN THE PLT WAS 14 TO 15 YRS OLD & THE EPISODES HAD BEEN ASSOCIATED WITH EXTREME NERVOUSNESS, SWEATING & PALPITATIONS. THE PLT'S MEDICAL CERTIFICATE WAS DATED 3/3/82.