Will getting a nissen surgery for GERD help me to sleep better at night?

Possibly. Many people with reflux have their worst problems at night when laying flat; sleeping more upright with pillows or even putting the head of the bed elevated on blocks can help. If the reflux is unresponsive to maximal medical management, surgery is an option. I strongly advise you to have a 24 hr pH study to objectively measure what is happening when you sleep before considering surgery.
Possibly. Reflux occurs commonly at night. If you wake up with severe heartburn or coughing, then antireflux surgery will likely alleviate these symptoms and help you sleep better at night.