Side effects after months of use

I’ve been on Gabapentin for about 6 months. I am currently taking 1400mg daily to keep my RLS under control. I have not had any known side effects since I’ve first started. Last night I got really dizzy out of no where after my second daily dose and my head continued to feel slightly dizzy the rest of the night and the next day. Now I am feeling nauseous. Can side effects of Gabapentin come on after being on it for months? I have not increased my dose or anything recently.