Get outside and take a walk if you can. Fresh air does wonders I find and the movement seems to help my digestion whenever I've been less that kind on my system. Drink lots of water and herbal tea - hydration is important. Foodwise I'd recommend sticking to whatever leftovers are closest to whole foods and don't make you feel heavy or weighed down even further. Definitely good to keep up all your other healthy habits too even if you're feeling less than stellar (sleep, stress management, sunlight, etc).