Update:
I drank a glass of water every half an hour for few hours before training and drank some more in training and didnt have any headaches.
For the gassing, I tried to relax and it worked! I had guy in my guard and focused on defending and keeping him from laying on me and it worked nicely. He gassed so badly after a few minutes and I easily transitioned to a mount
I noticed that when I tried to save my energy and not go all over the place for subs I managed to control and tap nearly everyone my size but I was easily outmuscled by bigger guys.
I´m around 165lbs and when fighting guys that are 220lbs I was in big troubles. When I had them in my guard they passed easily but when I was in their guard I couldnt pass, infact I wasnt even close! I should be happy though that they didnt submit me though.