I am fit and used to exercise a lot until I stopped a year ago. I decided to resume physical activities recently, but I noticed that it makes me feel much worse than before. I tried Brazilian Jiu-Jitsu for a few times (I did it for years before). In all attempts, by the end of the class I was feeling dizzy and very sore for the rest of the week. Later I decided to exercise by myself at home, however I still feel very sore a week after, after trying only one time. I heard it could be lack of water intake, but I take a lot of water over the day. I didn't change my habits significantly, so I can't understand what is going wrong. Should I see a doctor for that?
The simplest answer is that you are no longer as fit as you once were.
It will take some time to regain your lost level of fitness.
Other possible considerations (or combinations):
- You're not fueling well enough before you train (your training efficiency has changed)
- You're not hydrated well enough before you train
- You are deficient in something from your diet (electrolytes for instance)
- You're not sleeping well enough
- You're training too much out of the gate (you have to work up to it)
- You're changing what you're doing too frequently. The main reason people get sore from training is whatever they are doing is new. Also too much variety and a lack of consistency. BJJ is a lot of variety, and by extension takes a longer time to get used to the chaotic environment again.
More than likely a combination of those factors. You should see a doctor if establishing more consistency and making a few changes in your approach/nutrition, doesn't reduce the soreness/dizziness. The dizziness especially be a BP issue for instance.
Being sore for a week after doing something you haven't done in a year is very common. You did too much on your first time back. The bout of BJJ and the bout of exercise at home were also (likely?) completely different as I assume you weren't doing BJJ at home. Two different training stimulus, so ya, of course the exercise at home made you sore in a different way. Again, you also likely did too much your first time into it.
Try doing a bit less (like 1-2 sets of maybe 4-8 exercises at home, or only 15-20 minutes of BJJ) and gradually adding volume/duration or intensity.