While cervical thrust manipulation, repeated motions, and traditional mobilization all work well for an "Acute" Neck lock (mechanism debatable). Sometimes, your technique and patient preference are not tolerated due to sensitivity of the area. This is my go to technique for an "Acute" lock - patient wakes up with mod-severe pain and limited range mostly one side greater than the other.
The technique is rather simple. Apply a very strong traction with the patient holding onto the table so they don't slide. Stop when you see their feet dorsiflex, I estimate it's about 30-40# of force. Hold the traction and rotate to end range rotation away from the restricted side and continue traction as you return to neutral. Repeat toward the involved side. You may need to do 2 reps of this, but often that is enough to restore ability to load the involved side with much less threat. After, they can tolerated their own repeated cervical retraction and SB toward the involved side or rotation.