You are not strong!
That's what I repeated to myself in my first judo class, I have no intention of being pessimistic or discouraging you.
I went back to exercising a few weeks ago and it was doing well (that's what I thought), so yesterday I went to practice an experimental judo class. And man I just took a beating, the sedentary lifestyle hit my face as the arrogance watched everything eat popcorn LOL.
My blood pressure dropped and I felt very nauseous, at the end of the training the master asked if I was better and what I thought of the training, I simply replied:
Everything I went through in that workout was very necessary, it showed me how my 4-mile runs were nothing like that warm-up full of sit-ups and somersaults (they're the reason for my nausea). And as healthy as I feel, I'm nowhere near good stamina. While standing there on the mat I was reminded of my kung fu training, how light I was and my legs were strong, and today I'm only 10lbs heavier than then, but it feels like 30. Today 80lbs.
At the very least you will get your body quite sore, but there will be people there supporting you, rooting for you to overcome your limitations, and will accept you as a new member of the family.
Source: https://unsplash.com/photos/Yf1SegAI84o