I dare say they haven’t reviewed every reported side effect with you and the bizarre dreams is an uncommon one. But here’s a patient quote from drugs.com -

I’m so happy someone else is having the same issues . I started on gabapentin last Friday 100mg before bed… I’m having such vivid nightmares I can’t tell when I’m awake or sleeping. I’ll think I’m awake be looking at my room but it’s spinning and my eye site is blurry…