Yes it is possible to experience lightheadedness and even syncope. What I discovered during my journey was that I experienced symptoms I didn't consider were symptoms because I always felt that way after doing certain activities...I thought it was "normal"...but it was my "normal" due to Chiari but I wasn't aware of it. Once I learned more, I discovered that some of the "normal" feelings I had were in fact symptoms of Chiari.
Know you are not alone...please list your symptoms and compare to others here....There is a thread with a list of symptoms other members have experienced.
Here is a link to that thread-- https://www.medhelp.org/posts/Chiari-Malformation/Unofficial-Symptoms-List-/show/1192372