Hi Clayton and welcome to Dhamma Wheel!
I'm also going on a ten-day Goenka retreat next week! I've been practicing under Mr Goenka's instruction since 1985 and have done many 10-day retreats and numerous other retreats including shorter and long courses for 'experienced' practitioners - and I keep going back very regularly to sit or serve on courses.
What Zavk said is very true. For the vast majority of newcomers to Mr Goenka's courses, pain is the predominant sensation, and the sensation, whether it is painful, pleasant or neutral, is just an aid to develop insight. As someone recovering from substance abuse, you may actually find the ten-day course of profound benefit to you, as many others have before you. As Zavk says, drop any preconceptions you might have before attending.
If you have any questions regarding your upcoming ten-day course, please feel free to ask, privately if you want to, and I will try and answer any questions or allay any concerns you may have. All the very best with your retreat and I look forward to reading your contributions here.