I've experienced a few 4-day retreats and one 10-day Vipassana retreat, and for all of these, the first 4 days can be extremely difficult. Your body isn't used to not moving, and your mind isn't used to not thinking, unless it's going to sleep, so you can feel a lot of things that some people don't consider when signing up. A lot of people just expect or try to get into some state right away and end up feeling disappointed, but the mind does need those first few days to quiet down. The body, for me, was a lasting issue during the 10 day retreat. I had only done a 4-day retreat before that and didn't sit much beforehand. I'd suggest going to a few yoga classes before May if you can. If you haven't sat still for an hour before give it a try, you'll be sitting for 8+ hours a day. Emotionally it was hell. A constant roller coaster. Everyone can look so peaceful on their cushions and you might think you're failing and everyone else is in some beautiful state but the truth is most people are thinking the same thing. This was hard for me because I felt like I didn't deserve to be there and even at one point thought I might be crazy! I really expected to leave the retreat with a bunch of new insight and all, but the actual progress was much more subtle and helpful. By the end I could understand that I was not my thoughts which has helped immensely in practice and life. Spiritually it's like a recharge. You come back to the "real world" and not really feel like you fit in though. You may have a deep determination to continue to practice. My last retreat, it made me not want to leave a cave for the rest of my life, but it's not feasible, and those thoughts die down. You should however continue to practice everyday and use your experience as a reminder and motivational factor even when the honeymoon phase of retreat subsides.

Lastly, don't worry about ego death. As I said before the insights you get from retreat tend to be subtle and unexpected for what you thought would happen. Go into it with a little expectation as you can. It's hard not to go in without some, but just keep in mind that it won't be how you thought it'd be, and you'll come out the other side 10 days later pretty much the same person. Have a wonderful retreat!