My son's treatment is done on most of the right side of his face. Everyone reacts a bit differently, but typical for him is a lot of swelling that starts several hours after treatment and lasts for the 2 days following treatment. The bruising/purpura usually develops by day 2 (day after treatment), and is fairly significant until about day 4 or 5. It usually takes about 2 weeks for the bruising to fade completely. These time frames are individual. You may react much differently. It depends on the settings of the laser also.
We have had no scarring or blistering. With the lasers used currently, there should not be problems like this. Of course, it depends on the knowledge of the user of the laser. As for making it worse, I've never heard of that happening. The laser is tuned to treat the vessels just under the skin..causing them to constrict/shrink, thus reducing the blood flow to the PWS.