17. You are all sweaty, and you don’t know why
In most cases, sweat is a sign of high fever, but if your temperature seems normal, it’s even more concerning. Experiencing sweat for apparently no reason, such as an intense workout, could signal a heart attack, a pulmonary embolism, an arrhythmia, or an aortic dissection.
18. You have a stiff neck and a headache
Generally, according to Dr. Kino, experiencing a stiff nick without a headache is commonly associated with having a muscle spasm. However, if your stiff neck is accompanied by a headache along with sensitivity to light, it means that you could actually have an infection around the brain, a.k.a. encephalitis.
Note that encephalitis can be fatal when left untreated.