Drowsy not feeding normally is a matter of concern can be aspiration and infection. Better you get a physical examination as soon as possible

Just as we adult after vomiting feel exhausted similar such thing happened to child. If the child is taking feeds but little more sleepy then it is okay Urine frequency should also be above 6 in 24 hours. If this 2 are normal, then child will regain normal movements and activity within 6 hours or at the maximum 2 days. However in doubt, can take a consultation. If on breastfeeding, child is gaining weight and passing urine 6+ in 24 hours, then avoid unnecessary formula feeds.