justintoronto wrote:i've never been above 9,000 .. how likely is it to develop severe altitude sickness or stuff like HACE ? that's pretty freaky.
That's a good question and good to be aware of the symptoms. Odds of that go up the higher you go, and the longer you stay up high (without gradual acclimatisation), but a dayhike from 8,000 to 11,000 feet is unlikely to go beyond mild AMS, if anything.
Absent acclimatisation, if you do any hikes in the Sierra above 12,000, or especially to 13,000 feet and higher, chances of needing to turn back before summitting will increase. Taking Ibuprofen if a mild headache develops near the summit may help. I don't see this in your plans, but spending a night above 10,000 feet (or especially higher) without gradually acclimatising first would also increase risk.
Stay hydrated. Avoid alcohol and caffeine the day before and day of your hike. Drink more water than you usually do (it will be harder to stay hydrated up high and in the desert). If you start peeing clear several times an hour, you may be overhydrating. Snack frequently or stop for meal breaks on the hike. You will probably notice some shortness of breath and difficulty keeping normal hiking pace. Don't race up the mountain as fast as you can. Don't let your breathing rate stay slow.
For Telescope, sleeping overnight for free at Mahogany Flat (8, 200 feet) before the hike could be helpful, but if you get a headache there, sleep lower down at Thorndike, or Wildrose. Sleep low after the hike to recover (unless you feel normal, then Mahogany Flat may be fine). http://www.nps.gov/deva/planyourvisit/camping.htm
If you develop a throbbing headache and major nausea/vomitting, seek lower elevation ASAP. Here is an article with more details: http://www.summitpost.org/expedition-medicine/675753
Edit: camping link added and repaired