I have had some pretty tough reactions to antibiotics and herbs. However, I also have had pretty scary stuff happen when I wasn't treating. I had unconscious seizures and a big increase in neuropathy. Both came while I was off treatment. For me, the increases are almost always a definite herx but it's always good to check with your doctor especially regarding heart symptoms. Also, if I get any itching or hives I immediately stop taking things and call. That I never risk.
The heart stuff can be very scary. Anxiety is a major herx symptom for me and can become very difficult to deal with. When I'm herxing, I try alka seltzer gold and I try to go in to get an IV of glutathione which drastically helps with detoxing. For anxiety, I try valerian root and ashwagandha first and if that doesn't work and I need to get some rest, I take benadryl at 50mg.
A lot of people find that they have to start very slow on meds and ramp up gradually over a long length of time. So they might take Biaxin at 500mg for a month or longer until the herxing stops being so severe. You should ask your doctor about
that though to make sure it works okay to do that with your specific meds.