All the post and advice I'm reading are great, I'm from MD and was never at altitude before and went to Rainier in 07 to summit. There was no way to train for it on the east coast so I did a program with the guide service that allowed you to stay at Muir camp 10,000ft an extra night for acclimation before the summit attempt.
I will offer this, staying calm is very important especialy if you are solo. Altitude can be a bit scary with nausia, headache and a bit of panic can really make it worse. Decending if possible and gathering yourself with some food, water and rest will clear your head.