Sounds either stress related or developing MBD (Metabolic Bone Disease). Keep him in a quiet room where there isn't a lot of distractions - if you like and this helps... Cover 3 sides of the tank up with a dark material excluding the front view so he doesn't feel overwhelmed. Try to refrain on checking on him so much including handling if you guys are (Keep minimal as possible). Let him rest and try to give him a 'warm' soak tomorrow to help loosen his bowels to expel waste (15-20 minutes should do the trick).

The day temperatures are good that you have him at; how cold has it dropped since you've had a weather change. Does your pixie burrow completely under the dirt or keep his body out? Keep your frog on a daily feeding schedule, not all over the place. For example, since they're nocturnal - feed them at night every 2 nights at around 8:00-10:00 PM. At your pixies size they only need to eat every 2-3 days for 15-20 minutes.

Jcal mentioned about distilled water not containing beneficial minerals for them to absorb which is true. Since distilled water is produced through reverse osmosis it leaves pure H20. Buy Reptisafe dechlorinator at any local pet supply store - it will remove chlorine, ammonia, chloramines, metal traces, and additionally add calcium (Electrolytes) to the tap water.

Since the traces of calcium found in crickets after eating 'fortified calcium gutload' is minor, it's recommended to purchase a calcium supplement for dusting foods during the week. Calcium is useless though if it does not contain the Vitamin D3 in it since this essential vitamin is synthesized through a chemical process in the skin from the natural sun UVB wavelengths. For frogs, it's not recommended to keep them under UVB bulbs (UV radiation) - so that's why we supplement in the Vitamin D3 they lack in captivity that helps absorb and process the calcium throughout the body. Calcium w/ D3 should be supplemented every other feeding. It's also important to purchase a multivitamin to dust on their food once a week. Brands: Rep-Cal, Repashy, Flukers, T Rex, Reptivite.

If you're only feeding crickets, you should also be offering other foods in their diet. Earthworms and roaches are another great staple food. You can purchase earthworms priced a lot lower than pet supply stores at Walmart in the sporting goods sections. Just buy the ones that don't have any additives (Scents, dyes, flavorings, nitrogen).

Your pixie may be developing MBD (Metabolic Bone Disease) from several of factors you've mentioned. Cold weather impairs digestion and calcium absorption, lack of vitamin d3, and inadequate protein in their diet.

Don't listen to that guy at the shop, he obviously hasn't been keeping frogs. Unfortunately this will happen with employees leaving customers misinformed information about proper husbandry for these animals. From now on, come here for support. It's hard to determine whether or not your frog accidently ingested some moss, but that was the right move to remove it from your tank. Hopefully he didn't lunge at a cricket and ingest some of it which is very hard to pass given the right circumstances.