Why do I get light headed when I go from tying my shoes to standing up constantly? Should I be worried

Low blood pressure. You probably have very low blood pressure. When you bend over and then stand up, your body has to adjust to keep blood flowing to your brain with the sudden change in position. This is nothing to worry about unless you actually faint. Go slower. Drink more water. If you are worried you may faint, put your head back down and make an appointment to see your doctor.
Not enough juice. It is likely that your head/brain temporary did not get enough blood as you bending down while tying your shoes and then erect too quickly. I assume dyna26= young healthy 26 y/o gal? I would keep good hydration, sitdown to tie your shoes and get up more slowly...If symptoms persist, consult doc for evaluation.. Good luck.