There is a possibility that you are suffering vasovagal episodes in a very mild form or otherwise a dysfunction of the vagus nerve. This condition was made famous by an American President who choked on a pretzel and fainted. While the President was not a continuous sufferer of the condition, there are quite a few that suffer episodes like these with other triggers.
The vagus nerve is a nerve that starts at the brain stem and connects to the lungs and stomach. The mechanism that takes place during a fainting spell includes a drop in the heart rate when presented with a trigger and a drop in blood pressure. Some of the triggers of this condition include keeping the legs locked in a position for a long period of time, stresses, any discomforting experience like watching a painful experience, heat exposure, extreme emotions like rage, hunger, excessive nausea and vomiting, dehydration, swallowing, pressure on the vagus nerve, high altitude and sometime even laughter.
In advanced cases of the disease, sufferers may pass out only to recover and pass out again in a few minutes despite the absence of the original stimuli. The condition itself is not life threatening but the injuries that could result from falling or imbalance could be a cause for worry. In your case, the specific trigger appears to be the first few bites of food. Knowing that this is the trigger, you have to reduce the portion of food that you consume per bite, just in case you eat such a huge bolus that it creates a pressure on the vagus nerve. You must also keep your blood pressure high during these episodes. One of the methods that can be used is a method that is used by air force pilot as their aircraft reach high G forces. These forces tend to draw blood away from the brain and cause temporary loss of consciousness. This is can be avoided by tensing up the body and fighting the feeling of fainting. You can try this very technique by crossing your legs when you eat and tightening it while you are eating. This may not completely eliminate the feeling but should reduce the severity of it. It is also useful to increase your blood pressure using other means like a slightly increased salt intake to mitigate pressure drops that can sometimes occur. Eventually, you should be able to deal with the triggers and this in itself will help eliminate them as triggers of an episode.