What is the weather going to be like on October in Shangri-la?

During early Oct. the temperature would range from 5-16C or a little higher. The temp gradually falls and the lowest one would be -5C in the end of Oct. So it will be a little cold then. You may need prepare one or two warm clothes. Anyway, it is also nice to travel then.
For the High Altitude Sickness, I suggest you take some regular medicine in case. Upon your early arrival, good rest is needed to adjust to the environment.