If it's too low early morning, this possibly is not taking place, so glucose drops too low. If this is occurring, I suggest you try taking 4000 to 8000mg/day glutamine at night. This amino acid can be used by the brain in place of glucose, but being an amino it doesn't cause a sharp drop in blood glucose levels.
Sometimes, heat lightning isn't lightning at all, but a cloud reflection of lightning from a very distant storm. In other instances, it is regular lightning which has formed far off in the distance, making a flash instead of a recognizable lightning bolt.
If a lightning strike is a sufficient distance from the observer, sound from the strike will not be heard. These silent bolts are called heat lightning. Lightning bolts produce thunder, but the thunder sound does not travel all the way to the observer if the observer is too far away. The movement of sound in the atmosphere depends on the atmospheric properties of the air such as temperature and density.