PAWS (post acute withdrawal symptoms) begin after you have finished the physically painful withdrawal process. They can continue to occur for an extended period of time especially in users who have been on opiates for a while. PAWS generally consist of psychological problems like depression, anxiety, etc, which stem from chemical imbalances in your brain. The Dark Side is an excellent resource for those who are looking for information and support on this phenomena.....
exercise: This is the big one. Getting up and moving about is important for mental reasons as mentioned below, but vigorous exercise (whether running, weight lifting, or playing sports) can really improve how you feel. Even if you feel like utter crap and can't imagine getting out of bed, remember that you don't have the flu and breaking a sweat is a sure fire way to actually feel better. An exercise regime is also very important to getting over PAWS and maintaining your sobriety (never mind living longer and looking super sexy). You might as well start now when it'll also help with withdrawal.