A bearded dragon acts lazy or lethargic if the temperatures are not adequate enough. Low temperatures can cause a loss of appetite and activity levels can drop. Make sure to use high quality thermometers at each end of the terrarium (one in the basking area and one in the cooler area) so you can monitor temperatures.
How do I make my bearded dragon more active?
A great way to get your bearded dragon out and about is to use a special leash and take him for a stroll. This is an excellent activity for getting in a little exercise for yourself and some get-away time for your bearded dragon. A walk along the beach, or around your local park are always fun ideas.