I am on day 12 of 50mg of Zoloft. I am starting to feel pretty good during the day but?

This is normal and day 12 is very early. It takes at least 4-6 weeks for Zoloft to build up in your system and work properly. I live in Australia and it is commonly recommended and prescribed that during the initiation phase of Zoloft you take either a tamazapam or diazepam should you need it before bed. Insomnia, vivid dreams etc are all common. You may be feeling added anxiety about going to bed because of the intrusive thoughts. With Zoloft as it starts to work it addresses mood (at lower doses such as 50 mg) so during the day you may have increased mood but the dampening of anxiety hasn't started to kick in yet. Don't be afraid to take an anti anxiety that works on your nervous system like valium as this will be short term and get you through this teething stage. Once the Zoloft starts to do its job you won't know yourself but be prepared to be flexible and don't give up. It takes courage to do this but it is worth it.

Hi, geokar! Sometimes it can take a few weeks for the side effects to subside but they generally do. Sleep disturbances and intrusive thoughts are common side effects of Zoloft and other antidepressants and may be *normal* for you but do let your doctor know that you're having this problem.
As my friend, janie, has said I'm glad it's helping you otherwise. You're off to a good start and it should just keep getting better from here on in.

Hi geokar-
Sometimes meds that change your serotonin levels can cause changes to your dream state and in your sleeping habits. You can try to stay with it for a few more weeks to see if it lessens or goes away. The good part is that it is helping you during the day.