Ali
I don't know how much traveling you've done, but one thing to remember is that you can get up and move around the cabin whenever the seat belt sign is off. Talk to the flight attendants and let them know your situation. They are there to help you. Do not be afraid to ask them for assistance.
I have traveled a great deal over the years (as a Flight Attendant and passenger) both long haul and short haul.
I just came back from my trip to Seattle albeit only a flight of a little more than an hour and had no problems. The Flight Attendants were very helpful as were the passengers in assisting me with my carry on and getting my checked bag.
Good luck with your PT on Wednesday and your flight on Sunday! Have a great time in Las Vegas!