This is a very good example that even when the pain and swelling are gone, the underlying issue is usually far from healed.
It appears that the stimulation provided by the BFST was more than the injury was ready for. It is not uncommon for people to make the mistake thinking that "if some is good, more is better". This thought process causes people to start their treatments on level 3 from day 1. It is very important to start your BFST treatments at level 1 and only move to the next level after a period of several treatments where the warmth of the treatment becomes much less noticeable. Very few people ever move past level 2 even after a year of use. The instructions indicate that even on level 1, if the area gets quite warm then to stop and just do shortened (5 - 10 minute) treatments for the first little while. Over treatment can result in aggravated symptoms of pain and swelling.
There is nothing wrong with just doing a 5 minute treatment on level 1 the first time you use a BFST. If your body is good with it, you can increase the treatment time and power level gradually over subsequent treatments. When you are well on your way to being healed, you will be able to give yourself 20 minute treatments at level 2 without issue. Even at that point you may not be fully healed, but you will definitely be well on the road.
If your symptoms get worse following BFST, this does mean you need to let up on treatments though. You have to give your body time to heal as well. This particular user had an injury that only stopped hurting after 3 months. That generally indicates full healing will take over 1 year! In the case of severe injury this can be the case. BFST is designed to help and accelerate the healing process. With serious injury, even with BFST, the process can still take some time. Ultimately though, the most serious injuries can still heal with the proper care.
Respect the pain - it is there to guide you. Be vigilant. Be patient. You can get better.