it happens due to inability to change bp during  dat lil time..it is due to less oxygen goin to ur brain..it cn be worse n cz syncope..means transient shut down of brain activity czing black screen infront of eyes n lightheadedness..enough to fall u down to transient  unconsciousness..well dont worry since it cn happen to anyone depending on hw quickly body adjust to bp changes..so if a person who is odrwise normal ds squats veryy quick he too might hv dis so u give time to your body to adjust it..since u hv morbid obesity its really hard fr ur body to adjust sudden bp fluctuations. so fr nw do it slowly once u shed sm extra kg ur body might get a quick response so u must shed weight drinking apple cidar vinegar 5 ml twice with warm water n honey before exercise and drinking concentrated black coffee before exercise vl help u shedding weight u cn add dese apart frm avoiding junk food n taking extra callories also u shud use sugerfree wen u taking tea or coffee avoid sugar ,starch rich foods like potatos,rice fr sm time... quite food restrictions with lil exercise vl help u to get fit n prevent so many diseases attributed to obesity stay healthy stay happy