Thanks so much for your question! It's a little hard to answer with certainty without seeing pictures, but the most common reason I see patients with more swelling on one side the day after the treatment is if they tend to sleep more. Gravity happens! If you sleep sitting up tonight, that may be all it takes for things to even out.
Dr. Sieber also makes some great points on how treatment can be variable, but the lovely thing about the Halo laser is it is set up to create consistent and symmetric results.
Either way, be sure to reach out to your doctor's office so that they can see what is going on and follow your healing out to a wonderful final result.