25Mgs is a pretty small dosage. Going to 50Mgs a day shouldn't produce any adverse effects, but it kind of depends on the person. I used to take 150Mgs of Zoloft a day and for me that was the effective dosage and it didn't cause any unusual side effects.
Any change in meds can make you feel "different" at first...hang in there!
I am on Zoloft and when i was ramping up it did cause me Dizzy and anxiety before it got better!!! hang in there! Leslie