Hi .....I had a car accident last year someone went into the back of my car...since then I have had chronic head aches, tiredness and fatigue...now I have numbness in my arm and face....they gave me a MRI and they found i have an arachnoid cyst at the back of the head...2.8cm x 1.9cm x 1.1cm.....is this big ...they are now referring me to the specialist should I be worried

Summarized question: What causes arachnoid cyst?