I'll second babybird's recommendation regarding a doctor's advice and I'll also suggest walking.
If a lack of cardio fitness or mobility is preventing you from getting back into dancing right now, you might try walking to music with some choreography worked in. (No, I'm talking about that Leslie Sansone crap!!) I'm a fan of a lot of Jessica Smith's online workouts and can recommend her Walk n' Talk series* as a good place to start over. "How to Love Your Body As-Is" is an easy one. https://www.youtube.com/results?search_ ... +workouts+
If those are too easy, you can try her power walks (some of which are surprisingly tough), her HIIT stuff, circuit workouts, kickboxing, barre, the wide variety of strength workouts, yoga, and more. She covers practically everything, for all ability/fitness levels.
You could also get back into the groove with Up to the Beat Fit: the instructor, Gina, plays some great tunes and really has the moves. (I really DON'T!!) Some of her dance videos are set to a single song and are less than 5 minutes long, so if she's more your style, go for it. I don't recommend all of her toning/strength videos due to their pace, but hey--no one's perfect.
I could give you a run-down on a lot of other online instructors, and online workouts in general, if you wish.
In the 30+ years I've been working out (or not!), I've had some real ups and downs, from uninspired slacking off to plateaus, minor injuries, and long-term rehab. One important thing to keep in mind is that with a balance of patience and persistence, your body can do amazing things.
*Jessica always says "this is not a workout" during these 1-mile sessions, but if you're really just getting into/back into things, it can be! If nothing else, it's a good warm-up before a better stretch session. Regardless of where you are, give yourself credit for whatever you can do and whatever other steps you take.