I almost passed out five minutes into a yoga class. Please help :( I'm not quite sure what can be done about my health and fitness besides a diet. For some context, I am 22 years old, weighing 127kg, and am incredibly weak. Think "struggles to curl five pound dumbbells" weak. Due to my anxiety meds, food cravings are rather substantial. I decided to join a gym and take part in some of their low intensity classes. I started off with a yoga class. The class was scheduled to last half an hour but I had to give up in five. 

It was with quite a bit of shame that I had to pack up my mat and shuffle outside, seeing spots of light as I felt starved for oxygen. The room was full of folks much older than me, doing the yoga positions with minimal effort. I was unable to bend my knees in a lunge. 

Considering this abysmal strength and endurance, would any folks be kind enough to suggest a plan of action I could follow? How important is physical exercise to lose weight? 