Ben Roethlisberger says he actually LOST SLEEP over the way the Pittsburgh Steelers handled the national anthem situation on Sunday ... and wishes he wouldn't have stayed in the tunnel.

Steelers coach Mike Tomlin had said before the game that the team would "not participate" in the anthem to protect the players from having to take a public stance on the issue.

All but one of the players stayed out of sight -- the exception being offensive lineman Alejandro Villanueva (a retired Army Ranger) ... who stood on the field.

Now, Big Ben -- who stayed in the tunnel during the "Star Spangled Banner" -- says he regrets not joining Villanueva.

"The idea was to be unified as a team when so much attention is paid to things dividing our country, but I wish we approached it differently," Roethlisberger said.

"We did not want to appear divided on the sideline with some standing and some kneeling or sitting."

"As a team, it was not a protest of the flag or the Anthem. I personally don’t believe the Anthem is ever the time to make any type of protest."

"I appreciate the unique diversity in my team and throughout the league and completely support the call for social change and the pursuit of true equality."