The Ancient Times.

It wasn't just a few centuries before the current date that he woke up in the world, with no memory or understanding of what could have happened to him. He was already a fully grown person, but knew nothing. He already had some extraordinary powers and knew how to speak the language of the Sect people.

He was found by the Qi Clan leader, of the YunQi Sect and taken to his refuge, Fox's Burrows.
He was treated well, he joined their Sect at first, although his powers were not compatible with those of the other adepts.
He was often suggested to keep his skills secret and never use them, by the clan leader, but since he couldn't defend himself in any other way, he was often forced to.

Over 1200 years from the current time, a massive war among the Sects started. It lasted several centuries and resulted in the destruction of many sects. During that rough period, his powers became publicly known and he was literally begged to use them for the greater good. He participated in many battles and annihilated the opponents, but due to the fact his heart corrupting magic can be difficult to control, he also ended up accidentally harming people on his same side, which at first was tolerated. His powers gave a too big advantage to stop using them for just a few casualties, many more would die in a battle without him.
In few years, his powers helped to bring the wars to an end.
*Not all the fighting sects got destroyed, some were allowed to surrender.*

But the celebrations towards him didn't last for long.
Many wanted to use him for their own purposes or get their hands on his powers. He kept being questioned, framed and blamed for all sort of things, just to try to force him to reveal his secrets or offer his powers to a new master.
He never accepted and nobody ever believed that he really didn't know anything about the source of his uncommon powers. Soon enough, not even his closest person, QI XuanYu, defended him anymore.
Some people tried to stand on his side, but everything only turned out to be even worse.

A lot of good people got framed or accused of treason for taking his side and trying to defend him in front of the injustices he was going through, which resulted in a lot of unfair judgement and deaths too.
Xie and the few people loyal to him tried to escape and be by themselves, but of course the other Sects wouldn't let them be, they wanted Xie at all costs, but in truth, it was the Hori Sect that wanted him the most and not surprisingly, the clans that were the most fierce in the matter were the Hai and Zhi.

Eventually, he and his people got caught. He never knew for sure what was of his friends. He just know that his life turned into a hell of dungeons and escaping from a place to another.
After his final attempt to disappear, he got surrounded by people from Fuchou and YunQi Sects and got sealed in that cave. It was XuanYu's sword that was used for the ritual and him who stabbed Xie with it.

Xie didn't sleep for only one century, as he says, but at least 7 centuries.