Altitude sickness? Dehydration? Other?

Hey all,

While hiking up I had pins and needles in one leg while hiking which I kept stopping to stretch, this is a first for me, it went away after about an hour of stretching stops but I'm unsure if the stretching fixed it. Near the top I had a pretty good sized headache, before hiking to the summit I took some advil and layed down for a half hour/hour and it felt a bit better but was still there, on the way down it was still pounding. My vision/balance was a little off as I can remember looking over at something far away and sort of having it swirl/turn. I made a pretty bad decision while hiking when I lost a trail to keep going thinking "oh it's probably over there" and kept going for about a half hour/hour which is uncharacteristic of my style of hiking (though it might just be me being an idiot, I'll fully admit).

So, here's what I did. I live at sea level, in the morning I drove up to 6,500ft, then hiked within 4-5 hours up to 11,000ft. I've done this at a slower pace (hiking up) before a few times without any issues other than being dog tired. I chugged a lot of water (liter and a half) in the morning before going, brought a 3 liter camel pack which I sipped the entire way through, finishing as I was going to my car. Peeing during this trek seemed fine, mild coloring, this morning = heavy coloring after drinking another liter +12oz water after getting home. I ate oatmeal for breakfast, had three cliff bars, a can of tuna, three ounces of dried cranberries, and a half bag of jelly bellies while hiking (all but the oatmeal).

Any ideas what the hell happened? This is all new to me and the pins and needles is really weird when not sitting down. Any ideas or if you've had similar would be really nice to hear. Thanks for reading.