Insecticide spray without telling passengers until spraying started

Was on a flight from Johannesburg to Victoria Falls. As we are taxiing , the flight attendants tell us to cover our faces, noses and mouths as they are required to spray permethrin. They claimed it was approved by WHO so passengers shouldn't be concerned. It was a battle to find out from the flight attendant (I have her name) what the chemical was. She showed me the can, but wouldn't let me see that the ingredient (and whatever else) was permethrin. It wasn't until I told her I was recovering from lung cancer and needed to know so I could tell my doctor what I was inhaling. Then she was very nasty and condescending when I demanded to see the can. She left it with me but told me that I would be subjected to some sort of discipline if I didn't give the can back to her. In addition, permethrin will **** small animals and cats. If we had been told up front that they had to do this, our group could have been prepared. My doctors had given me face masks if I needed them. I understand why they have to spray the cabin. Also on this flight was a woman who was extremely sick. She was coughing up mucous, not covering her mouth, letting all the particulate spray around us and had sores all over her mouth. Of course the flight attendants had no problem with this person and gave people sitting around her a hard time about moving away from her. The least the should have done was move this passenger to a row by herself thus isolating her. There was room on the plane. We saw Zimbabwe medical take this woman immediately when she arrived at immigration to a quarantine area. I would sure like to know what she had. I have this woman's seat number, etc.