There are a lot of symptoms that might manifest themselves during an impaction. For those who don't understand what an impaction is, it basically is an obstruction of non-digestable material in the digestive tract. Generally it is caused by accidentally eating their cage bedding (wood chips, bark, calcisand, rocks, and so forth). Other causes are overfeeding, improper cage temperatures, and dehydration.
Anyway, symptoms include:
Irregularity. Namely constipation, but it can also be other things - like straining to go but not passing or passing very little.
Difficulty breathing or acting almost like some kind of a seizure.
Regurgitation of a meal.
Paralysis is also possible.
In my experience treatment is not always very effective. Prevention is worth a pound of cure in this particular case... but anyway, possible treatments:
First correcting the husbandry issue that caused the impaction in the first place.
Soaking in warm water 2 or 3 times a day for 10-20 minutes.
A good herp vet could remove an impaction surgically, or possibly prescribe a laxative depending on the severity of the condition - getting a gecko to take medicine is easier said than done
Treatment of an ancillary infection may also be necessary.
Most people find it rather gross, but its rather important to inspect your pet's poop. It can tell alot about their overall health before outward signs are even apparent.