It is your neck posture that is important, especially when relaxed.

If you worked in construction on your feet all day, would you expect to continue working if you broke your leg ?

Your brain needs time to heal.

Regarding exercise helping recovery. The value of exercise is supporting good blood flow to the brain. If the exercise causes any symptoms, it is too much effort. There are ways to stimulate moderated blood flow without risking a serious increase in symptoms.

My brain is too tired to go on and explain this further.

At this point in time, you should just take it slow and easy to let your brain recover. YOU ARE EXTREMELY EARLY IN YOUR RECOVERY.

When you are still struggling 6 weeks after your injury, you can start to consider your symptoms prolonged and due a diagnosis of PCS.