sinusitis
"Omg. This medicine is scary. Had a very, very bad sinus infection. I was desperate for relief.  A day after taking this medicine, I felt a stiffness in my neck. Thought nothing of it, maybe I slept on it wrong? Switched pillows. Next night, worse. Three days in, could barely stand the pain in my neck. Then it hit me that the medicine was causing the muscle/tendon issue. Also, this medicine made me seriously feel out of it. I had to stop after 4 days. I'd rather deal with the sinus infection."