I almost never do sprints on flat ground. I'm pretty fast (from hill sprints maybe?) and am honestly afraid of face planting so I never run hard enough on flat ground. Uphill I don't have that worry because I can't naturally go as fast due to the incline.
I used to try to go for 10, but the workout would get way too long so now I jsut keep it to 5-7 or so and yeah I've felt pretty light headed after them, sometimes it gets a little scary.
I also don't get them in as often as I should, but I don't go a month without at least one session.
I used to seriously post here, now I prefer to troll.