A stationary bike should be OK but do not push to a level of increased symptoms. You seriously need to get help with your neck. And, stop cracking your neck, at least until you have had a neck expert help you heal your neck. Some experts believe self cracking creates a degenerative condition that causes a need for even more neck cracking. Some believe it leads to osteo-arthritis.

For some, it becomes an Obsessive Compulsive Disorder behavior.

Your neck issues could be a big cause of your symptoms. 80% of concussion symptoms are neck related.

Here is a web site that explains the problem and how to end it. It takes serious discipline to allow the neck to heal.
Massage and Bodywork Magazine for the Visually Impaired