First, you need to calm down and take a chill pill. You chose to accept this job offer and move. What you are experiencing now is...Fear Of The Unknown. You are scared about leaving everyone and everything that is familiar to you. It is starting to hit you that you will be in a town where you won't know anybody (Are you Greek? Check into your Houston area alumnae club). Be social - this new job will require adjustment, but think of it as being like freshman year of college-all over again. Every new life stage requires letting go of the past & embracing the future.
Congratulations on the new job! For a big company in Houston to want you, you must be special. Treat yourself like you are, and embrace the new possibilities that Houston offers. The apartment? Don't sweat the small stuff. Call some apartment rental companies and have them do the work. Think of the excitement of starting over, and start to look forward to your move.