Patriots Coach Terrell Williams Suffers Medical Scare on Sideline During Practice

10:52 AM PT -- Good news from New England -- the Patriots just revealed Terrell Williams experienced dehydration during Monday's workouts and is now doing fine.

A scary moment unfolded at New England Patriots practice on Monday ... when defensive coordinator Terrell Williams -- who recently returned from health issues -- suffered an apparent medical scare on the sidelines.

The incident went down on the training fields behind Gillette Stadium, where Williams -- who was hired in January -- suddenly went to the ground, according to reporters on the scene.

Several spectators shared photos on social media showing Coach Williams on the grass as medical personnel provided aid and rolled out a stretcher.

Thankfully, they also noted Coach Williams was eventually able to get up on his own.

This incident follows Coach Williams' extended absence from the team during the spring due to an undisclosed illness.

Williams, 51, hasn't revealed the nature of the health issue.

"Big T is here, ready to go. He's been out on the field with us the last couple of days," head coach Mike Vrabel said last month.

"Players were excited to see him. I was excited to see him, and we'll move forward."

Williams has been coaching defense since 1998 ... and got his NFL debut in 2012 with the Raiders.