Getting "gassed" is typical when first encountering any new physical activity. Funny how some of the BJJ'ers jump in and cite to it as "proof" they are doing great things. Total bullshit.
I could take any MA guy ... toss them into a swim pool and have them start rapidly pulling out laps of the overhand free style stroke. In a minute or so they will be gassed.
I could take any "great BJJ" guy, put him in H'ung Ga's 1000 Pound Horse Stance and the guy will be falling on the floor from shaking within a few minutes.
People say they are in "shape" ... for what? Being in "shape" is target activity specific and it is specific across a wide range of parameters.
Peeps tend to focus on muscle recruitment patterns when getting into "shape" for their activity of choice. That's a good start but not good enough. There is also the matter of intensity level when practicing - training as that conditions the specific metabolic energy pathways employed. Lactic acid clearance rate is an important consideration in line with the above.
Depending on your age ... you probably have about 30 - 45 days of "body hardening" to undergo. It's important that you not miss any classes and walk through the pain. Your body will respond accordingly and make the necessary changes to meet the activity specific imposed demands.
Lay out of class here & there because you aren't "feeling right" and you just prolong the hardening phase. Go through it ... go through it strong and you will emerge "in shape" ... for doing BJJ. John