Check all your possibilities. Clean, sterile water that has an air pump or water filter. Temperature should be around 70, no lower than 65, no higher than 75. Humidity should be around 80, not so thick there's no air flow and they can't breath in it, not so light the land portion is actually too dry.

Lighten up on the feeding if they're not eating but keep something available. They can go a long time without food, especially in cooler, hibernating conditions.

Possibilities of looking down in the weather are anywhere from hibernating for cooler conditions to stress, injury, infections, diseases, parasites, intestinal and/or external, or things like impaction from swallowing food and/or substrate like gravel.

Even toads need calcium and vitamins they should be getting from gut loaded feeders, crickets that have ate well themselves. On occasions I go as far as to give them crickets I powdered with herptivite and repti-cal. It's intended for my geckos but has done just as good for the toads.

Too much stress like over crowding or too much fussing/handling. Even toads enjoy their solitude.

The water is: dirty, foamy, murky, slimy, the ammonia is too high, the toads own toxicity in the water is too high.

Bloated	Mine do seem to fatten up for breeding, as if my females must be 'pregnant' with eggs. I think bloated but not eating would be more like something else is wrong like disease, parasites or an impaction.
Clouded/Unhealthy looking (skin, eyes, nose)	Even bombina's can get aquarium problems like stress coat, ick, fungus, bacterial infections.
Hibernation	The toad is barely eating, dark, hidden and crouching or nose to the ground. This is a classic position for a number of reasons. One is hibernation mode. The temperatures for the tank are 60 degrees or below and they've become sluggish and may even be trying to dig to bury themselves. The temp can be safely raised with an under the tank heating pad. Using a tank hood, the humidity will also raise and warm.
Humidity	Humidity should be around 80% with adequate air ventilation. Not so humid the air is stale and hard to breath, not so low the toad actually dries out or the land substrate dries out or isn't moist enough at all. Tank hoods are preferable over screen top covers for keeping humidity, going as far as getting a vivarium humidity fan if necessary for proper air flow. A plastic hood would be more giving about ventilation than a glass covering.
Impaction	Impaction is caused by the toad ingesting something and it has become clogged in the intestine. It can be anywhere from a build up of the exoskeletal shell of feeders like mealworms to accidentally swallowing a stone of aquarium gravel, sand or other substrate. A sign of impaction can look like bloating and loss of appetite.
Intestinal Parasites	Parasites will lay eggs in the potential insect. When it is eaten the eggs will hatch into the new host and come out through their fecal matter, waiting for another insect to come along and ingest them yet again as eggs. These parasites can just overrun a toads intestine and make them very sick up to death. The more you gather feeders from your backyard, the higher the risk becomes that your toad will carry parasites.
Lighting	Perhaps you have provided them lighting and they don't like it, constantly wiping at their eyes if not hiding all day long until the thing goes off. If just to look nice and see them by, a tank would only need fluorescent, cool white tube/bulb or blue tube/bulb lighting somewhere like 10 watts for 10-15 gallon, 18 watts for 15-20. It'll help the plants grow but not bother the toad with a bright light.
Metabolic Bone Disease	Looking hobbled, like they're hopping and walking around leaning to one side like an old lady with a heavy hand bag. Thus far the only thing I've found of this problem is prolonged calcium deficiency.
Stress	The toad is barely eating, dark, hidden and crouching or nose to the ground. This is a classic position for a number of reasons. Stress can come from being over crowded, handled too much or too much keeps going on inside the tank itself or for other reasons like illness on top of stress, trying to find a corner to themselves and just withdraw. Even toads enjoy their solitude and space and should be given that opportunity with plenty of room, places to hide and ample routine and calm.
Temperature	Temperature should be around 70, no lower than 65, no higher than 75 for a comfortable toad. The temperature will also affect the humidity. The higher the temperature, the more difficult it will become for a toad to breath. If it's too hot, they may turn to seeking out anything cooler and try to get lower such as spending more time at the bottom of the water or burying. If any heating is being used on the tank, it should be allowed a 'cool' period by being turned off such as at night or every few hours for a sufficient time things cool down without dropping past 60.
Water	The water should be changed regularly, by at least every month. It should be clean, steril or distilled water that is well aerated by air pump, water filter and/or water plants. Using things like sphagnum moss and activated carbon help keep things balanced. There are also various kits for checking levels of things like ammonia, acidity and/or php. Toads absorb water through their skin as their way of drinking it, making them super sensitive to the health of the water itself. Basically anything in the water is going to be in them as well.

Potassium permaganate is used as an agent to clear clouded aquarium water. It kills all bacteria, good and bad. Some aquarium medications include it in ingredients that can treat a tank to clear it of bacteria, fungus and parasites.