The 32-year-old suffered a knee ligament injury in January 2008 playing for West Ham United's reserves.
Collins says he was "virtually in tears" as he feared the worst during a scan on the injury.
"That's all that was in my head. I'm thinking this is never going to be the same again," he told Sport Wales.
The Newport-born player added: "I remember at my age looking at the fact that a cruciate knee injury - you used to see players not come back from it."
Collins made his Wales debut as a 20-year-old in a youthful team fielded by then-manager Mark Hughes for a 0-0 draw with Norway in May, 2004.
The former Cardiff City player says injuries have restricted his international appearances, but is relishing what lies ahead in France in the summer.
"I think I made my debut when I was 20 maybe. I am 32 now and only to be on 46 caps is not enough, really," Collins said.
"I've pulled out of a lot of games through injury and I was out for two years from international football with my knee."
Collins says "persistent calf problems" have also limited his Wales career.
"Every time there was a Wales trip coming around I seemed to be out," he added. "I wasn't playing at my club and obviously I was missing the Wales games.
"So to be involved now still, at 32, and having touched this successful (Welsh) period and enjoying it more than I ever have, is great.
"A while ago, looking at my Welsh career I thought it would probably never happen and to be involved and hopefully going into it (Euro 2016) playing well in a tremendous Welsh team is very exciting."
Watch Sport Wales, BBC Two Wales from 21:00 GMT on Friday night or catch up on iPlayer.
Wales defender James Collins will go to the 2016 European Championship this summer having feared eight years ago his playing career was over.