Maybe your hormones are acting up or puberty?
Interval training maximizes cardiovascular benefits, so it can quickly increase stroke volume, making your heart stronger, and more efficient. It also decreases your risk of heart disease and high blood pressure.
True because they can help you through it
It is use by Eye Care Professionals To check the eyesight of a person.
If u would have visited a eye care centre u would have noticed a chart like this--
If a person can see all the letters from a distance his eyesight is Perfect.If that person misses a letter or a line from the grid eye treatment or spectacles are given to the person for improving their eyesight
The nervous system is what i'd say. Are there any options?