If your chiro was using the Twist the head and pop the neck adjustment procedure, he was likely being too aggressive. It is fine for C-3 and below but C-2 and above will be stressed by such aggressive treatment. The inflammation that aggressive treatment causes can trigger inflammation and poor blood flow and poor breathing during sleep. These issues will cause nightmares and stressful sleep. The resulting poor quality sleep with trigger cognitive and memory issues. Word finding is a common struggle.

Traction and gentle mobilization helped me. Both my chiro and PT used it.

You may need to find a different chiro who has a better understanding of C-1 and C-2. There are chiro associations that teach only C-1 and C-2. NUCCA.org is one. upcspine.com and others explain it. Goodle upper c spine or upper cervical spine.