I've been to the vet enough times that I know the "drill" for assessing sick beardies. I often get phone calls asking me for advice and I find myself using the same questions. I thought I'd post them here for you.
Any time your beardie is acting strangely or not normal, answer these questions FIRST:
1- What's the heating in his tank?
There should be a hot basking area of 95 to 105 degrees. The cool side should be around 80 degrees during the day and no colder than 70 degrees at night. A beardie that is too cold cannot digest his food properly, will not eat, will not poop, and will slowly become sicker and sicker.
2- Does he have a UVB light?
EVERY BEARDED DRAGON MUST HAVE A UVB LIGHT!!! If you do not, you are dooming your beardie to a slow, tragic, painful, horrible, miserable death. They will NOT get UVB rays through your windows in your house; your windows filter out the light. The cheapest place to get UVB bulbs is on Amazon.com. You can pick one up for under $10.
3- When did he poop last?
A beardie who is not pooping may be impacted in their guts. Give a warm bath daily (or several times a day) to help them poop. The longer their food is inside them, the harder it becomes and the harder it is for them to get rid of it. Some beardies poop daily, others every few days. I have a female who prefers to poop once a week and in her water. More than weekly is not healthy for the beardie. Weekly warm baths will make a difference.
4- What substrate do you use in your tank?
My vets recommend using astroturf in the tank bottom. You can buy it cheaply at Home Depot (it comes 6 ft wide) and cut two of them for your tank. Keep one in the tank and one as back up. When the beardie poops or makes it dirty, you swap the dirty one out for the clean one. The astroturf is super durable and is perfect to put outside so it can be "sun bleached" to kill germs etc.
Sand -- even calcium sand-- can become impacted in your beardie's guts (though some beardie owners will debate this). Reptile carpet is very expensive but works fine if you want to spend the money. Another option is to get indoor slate tiles from a home improvement store and cut them to fit your tank (the store will usually cut them for free). Slate is easy to clean and has the bonus of filing down your beardie's nails. It will just make your tank very, very heavy.
5- When was the last time your beardie had anything to drink?
A dehydrated beardie will be lethargic and shrunken looking. Every adult beardie needs a weekly bath; juvenile beardies should have a bath every other day; baby beardies should only be misted with room temperature water. Give your beardie a warm bath for at least 20 minutes and see if he perks up after.
6- When was the last time your beardie had direct sunlight?
Direct sunlight is a great thing for your beardie! It can do more to help build calcium & vitamin D levels than any other supplement or light can. During the summer, beardies can go outside every day. Be sure to give them an area of shade and water. I have a rat/guinea pig cage on my back patio that is partially covered with leftover strips of astroturf that my big boy Max likes to stay in. He adjusts his position to keep himself cooler/warmer and is quite happy being outside even when it reaches 100 degrees here. Remember that beardies are desert animals and like the heat.
NEVER put them in a glass tank outside. You will KILL them very quickly. Use a wire pen like a rat cage or a bird cage that allows air to pass through.
7- What are you feeding your beardie?
Juvenile beardies need 75% protein and 25% greens. You can feed them calcium dusted or gut loaded crickets/mealworms/roaches daily. Once they hit 1 year, you need to transition them to 75% greens and 25 % protein. Most beardies I know do not like making this transition. Eating crickets daily is like feeding your kids mac n cheese & hot dogs every day-- tasty, but not very healthy. Your beardie may do a "hunger strike" for a few days (even a week or two) to protest the new healthy diet. Eventually he will start eating again and he will be healthier for it. Too much protein in an adult beardie will fatten up their livers and shorten their lives.
In the winter, beardies tend to stop eating and being active. It's called "Brumination" and it helps them to stay healthy. Never fear, after a few weeks, your beardie should perk up again. Other times, a beardie can go a week or so without eating. Sometimes that is a sign that something is wrong and sometimes it's just your beardie taking a break.
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If you can answer "yes" to the questions above and your beardie still isn't acting normally, there may be something more serious going on. Your best bet is to find a reptile vet and take your beardie in.
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My vets like to say that outdoor time is one of the best things you can do for your reptiles. Summer is the perfect time for outdoor time so USE IT to make your beardies healthier.
If you have any other questions, please post them below. I'd be happy to try to answer them. :)