Small amount that is used to be drawn for blood work should not affected your body as much unless you have circulation problem, low red blood cell count or your body baroreceptors (receptors that measure your pressure and rely info to the brain) are extremely sensitive. Usually symptoms you describe is when people loose a lot of blood. Certain volume of blood (6 liters) circulates your body. Red blood cells carry oxygen to the vital organs (brain, heart, lungs, renal system, etc, etc) and remove co2. Any time volume of blood gets affected few things will happen if brain senses that oxygen supplies are not being sufficient. First. your heart rate will increase to circulate blood faster. Remember now your volume is less so faster turn around should bring equilibrium back. But since now your heart rate is faster, heart which after all is a muscle has an increased demand for oxygen which means that your respirations will increase as well. Last thing that will happen is vasoconstriction which is term we use when your arteries and veins decrease their lumen (diameter) in order to increase the pressure that is already low due to the loss of blood. That's why people with severe blood loss are cold and sweaty. Little capillaries on the outside keep shutting off one by one keeping blood out of unimportant organs (like skin) and maintaining fluid supply to important stuff.

Being lightheaded, dizzy or tingling is normal when your brain has too little oxygen due to dropping supply secondary to blood loss. It is also the same way you feel when you hyperventilate or there is too much oxygen there (anxiety, panic attack, hyperventilation). What I assume may have happened is that you gave some blood, there was some drop in the volume, your body overreacted and out of the sudden your brain got little too much of the oxygen which caused dizziness and being lightheaded. Or just vasovegal response... Mind you this would be my vague explanation without me knowing you medical history, vital signs, etc..

Now to combat blood loss in the field is nearly impossible. First of all bleeding must be stopped (kind of hard to do for internal bleeding). There are no over the counter available products for us to replace lost blood. Short of blood transfusion there is nothing that can save you. In the field we pump people full of fluids to maintain their pressure and circulating volume but our fluids have no means to carry oxygen. If you are with somebody who suffered sever blood loss and they are going into shock and the ways to treat the socks are: lay them down flat, elevate their legs, keep them warm and provide with oxygen.

Adults metal status and reaction to blood loss is a steady down line. They progressively get worst until they crash. With children their bodies will compensate very nicely for a long period of time for blood loss (healthy heart and excellent circulation) until they cross a crash point and deteriorate in a matter of minute. It’s important to remember that because it is very easy to overlook a serious blood loss with the child,