Why do I feel the need to drink more ?

When I drink, I usually drink what I have to,to get me going in one go. So that’s about 100ml of alcohol. But when the buzz kicks in I feel a sense of fear almost that my drunkness will go away and I will sober up (being sober is a nightmare for me at the moment) so I drink more. This almost immediately causes me to vomit and it’s just not a pleasant experience.