Why is it if I lie down quickly that my heart rate drops drastically, and makes me feel light headed and short of breath? I almost feel like passing out, happens daily.

It's possible that your condition is related to orthostatic hypotension, which occurs when there is a sudden drop in blood pressure when you change positions. When transitioning from sitting or standing to lying down quickly, the body does not have time to adjust appropriately and this can cause a sudden decrease in blood pressure. The low blood pressure can then lead to lightheadedness and shortness of breath as well as other symptoms such as nausea, blurred vision, dizziness, and fainting. To help mitigate these symptoms it's important to take some preventative measures prior to abruptly changing position such as avoiding crossing your legs while sitting and avoiding standing up too quickly if you've been seated for some time. Additionally, sit on the edge of your bed before lying down so that you are able make an easier transition without putting strain on your heart rate or blood vessels. Lastly ensure proper hydration by drinking enough water throughout the day may help reduce lightheadedness during positional changes.