The six-times Pro Bowler said he had lost the feeling in his extremities "three or four" times since entering the NFL in 2000, the final one coming in October against the Carolina Panthers.
The 32-year-old Samuels told a news conference he had been born with a neck condition called stenosis.
"When I get hit a certain way, I lose power in my upper extremities, which is what happened to me last season against Carolina," he said.
A helmet-to-helmet hit with a defensive lineman during the Panthers' 20-17 victory marked the end of the road.
"Right when I hit him, everything went numb up top and I fell over and I knew I had had another episode. I went on the sideline, prayed about it, thought about going back in the game. The Lord led me to sit tight and I did.
"That's pretty much it."
Samuels said he was satisfied he had been able to play in the NFL for so long.
"Some doctors predicted I would only play six or seven years in the NFL, but here I am 10 years later having attended six Pro Bowls -- God has truly been good to me," he said.
"Mentally, I've been preparing for this a long time so don't you all feel sorry for me."
Since the NFL and the players' union have been unable to reach a deal on a new collective bargaining agreement, the upcoming season will not have a salary cap.
(Writing by Steve Ginsburg; Editing by Peter Rutherford and Ian Ransom)