The pilot's decision to attempt a mission at night with known en route weather conditions below operating minimums, likely due to self-induced pressure, and then continue flight beyond the alternate landing airport as weather conditions deteriorated, which resulted in the pilot experiencing spatial disorientation. Contributing to the accident were the pilot's fatigue, his failure to recognize that mist had formed on the inner surface of the windshield, his complacency due to the effectiveness of the night vision goggles, and his failure to use the radar altimeter.