Depends on the reptile and how it's treated. With snakes honestly it just takes them getting used to being held again. Very few reptiles are vicious or aggressive, just highly defensive. So just daily handling and they will be 'tame' and used to you within a few weeks, depending on the personality. Some are tame even if you never hold them in their whole lives(most ball pythons), some you can hold all the time and they just will always be nervous!
For instance, we stopped playing with our leopard geckos for a while, stuff got in the way, we had sick animals, etc. They were fed, but we didn't maintain tameness. They got really skittish(think the scared lizards you see outside of a house), but after a week of getting them back into handling they were cuddly and calm again :)
Reptiles don't need the attention, their brains don't function like other animals--they don't get sad, they are just happy if they are warm, clean, and well fed.
A snake that was treated as aggressive(taped mouth, jerked around, maybe even beaten) will become aggressive and need very special care often times. Sometimes they can recover from the trauma, sometimes they just have to be special pets!