Studies show that insomnia is caused by low GABA levels. [5] When there is not enough GABA present in the brain, the areas that GABA slows down keep on going and the activity doesn’t decrease as it normally would when the body winds down. GABA has been shown to positively impact deep sleep, the most important type of sleep we need. So even if you can fall asleep, a GABA deficiency may reduce the amount of deep sleep your body gets.