This is not true. While a 104 fever likely indicates a severe illness or infection the body can safely have a fever in the 104 to 106 range. It’s around 108 that brain damage becomes a concern and that is usually also due to environmental factors like a kid being left in a hot car.
If you feel your calf cramping up you should sit up in bed, straighten the troublesome leg, then grab your toes. I think it’s called the seated toe touch.