In dengue after 3-4 days after infection, there is internal dehydration in the body. Therefore, you should only focus on rehydration in the body for every 15-20 minutes using 3/4th glass of fruit juice, lemon water, coconut water, salt+sugar water, vegetable soups, etc. Also check when the patient has gone for urination. If he/she has not gone for more than 5 hours, then it indicates dehydration and there should be immediate rehydration for every 15-20 minutes. In severe dehydration, one should be hospitalised for IV fluids.
As regards the yogasana, one should prevent exercise/ yoga for this duration. Just make sure that there should not be dehydration in the body during dengue.