THE AIRCRAFT DEPARTED BEFORE DAWN FROM A PRIVATE SOD AIRSTRIP OWNED BY THE PILOT, AND COLLIDED WITH TREES SHORTLY THEREAFTER. THE PILOT'S WIFE SAID THAT THE AIRSTRIP WAS NOT FOGGY WHEN HER HUSBAND TOOK OFF, BUT THE WITNESS REPORTED THAT THE FOG AT THE ACCIDENT SITE PREVENTED THE SHERIFF'S DEPARTMENT FROM LOCATING THE WRECKAGE, 100 YARDS FROM THE WITNESS' HOUSE, UNTIL ABOUT 0700. THE NEAREST STATION REPORTED IMC CONDITIONS. THE PILOT DID NOT RECEIVE A WEATHER BRIEFING. THE INVESTIGATION FAILED TO DISCLOSE ANY AIRCRAFT SYSTEM MALFUNCTION OR FAILURE. THE PILOT WAS PROPERLY CERTIFICATED AND INSTRUMENT RATED. THE PILOT'S INTENTIONS WERE NOT KNOWN. HOWEVER, HE WAS FLYING TOWARDS THE APPROACH END OF HIS AIRSTRIP. AN AUTOPSY, TAKEN WITH MEDICAL HISTORY OF THE PILOT, INDICATES THAT SOME PHYSICAL PROBLEM MAY HAVE PROMPTED THE PILOT TO ATTEMPT TO LAND IMMEDIATELY.