Is it okay to feel lightheaded and dizzy after physical activity?

1) When I do a 3-mile or 5-mile run, I run for time and try to finish with nothing in the tank. The closer I get to the end, the more I push myself, because I know I don't need to sustain the effort much longer. When I stop running, I suddenly get very light-headed and dizzy. It never happens while I'm running. I walk briskly while I'm warming down, but that doesn't prevent it. Why does this happen? Is it dangerous?

2)  Sometimes after jogging a while, or cycling a great distance, my head begins to spin and I feel as if I'm going to pass out. Is it normal to have feelings like these, and if so, how intense should these feelings be?


Can our relationship survive summer break if we haven't had sex yet?

I am a 19-year-old college student and am seriously involved with my boyfriend who is a 20-year-old college student. We have even talked of getting married someday. Our relationship is very close and we talk about everything, and he is very wonderful and supportive. I feel very committed to him and would really like to have sex with him. We have tried twice, but it hasn't really worked out because my vagina is too tight. I am pretty sure the problem is just that it needs to be stretched more, because I have been to the gynecologist and don't have any infections. He says that he is okay with whatever we do and that he loves me no matter what, but I still feel guilty about not being able to go all the way. How do I get over this guilt? I will be leaving college for the summer soon and we will be separated for awhile and I want to make sure that our relationship is as solid as possible before I leave so we have the absolute best chances of surviving the summer!