This is a heck of a difficult question impinging on some highly technical areas. I'm not qualified to answer it, but I'll try to point to some resources.
I think it possible that the steroids cover up symptoms but don't address the root of the problem. I don't know if anyone has successfully tried to address Bell's Palsy with a paleo diet. However, I would definitely try googling "paleo bell's palsy" to see. I think you might also make your way over to Robb Wolf's site, find the search box there, and search for "bells palsy" across his site.
I'm not clear why the doctor wants you to do so much cardio exercise. Is it supposed to help weight-loss or what? If it's hurting you, I think you should tell him or her. I guess 30 mins gentle exercise a day is good for most people, but perhaps you could do something else - swimming?
Bangalore's in India, isn't it? I'd have thought you could find better yoga teachers there than in the West. Would that be an area worth looking into?
I wouldn't worry too much about weight-loss. It tends to drop off if you cut back on carbohydrate, particularly refined carbohydrate, and get plenty of sleep. Enough sleep, in a room that's as dark as you can make it, has a huge but generally unrecognized effect on this.
I'm sorry I've nothing better.