I’ve noticed that in the past, if I’ve gone days without talking to people, I tend to feel mildly depressed and upset.

In this situation you will be at a retreat and have enough to keep yourself occupied, and you will be surrounded by people doing the same. You might discover that it is actually a very calm and supportive atmosphere, with respect and space and patience.

Is loneliness during the retreat something that you experienced? If so, how did you get through it?

I used the technique on it and discovered that it was impermanent just like everything else and I continued on using the technique on the next thing that showed up in my mind, etc.