Hi Kaz
It happens to the best of us, BUT, you must try and nip it in the bud straight away....You have come so far and you dont want to put anything back on again because that will just make you feel more depressed, then want to eat, and get more depressed, well, a downward spiral.
Keep remembering the reason why you are having these shakes!!! It isnt for long and eventually (well, for the rest of your life) you will be able to eat again. This is only for a short time and worth the commitment.
Dont look back, just keep looking forward to the day when you are almost at goal. That feeling you had after you ate and felt you couldnt stop...was it horrid??? I bet,,,well, I always say BOTTLE THAT FEELING....it will take you a long way and you wont want to feel like that again in a hurry.
Keep positive and moving forward..what is done is done...This can actually be what you needed and will give you more determination to make it and to get to goal asap.
Have a great week, and remember, tomorrow is a new day and a new start and YOU HAVE DONE SO WELL SO FAR.
Take care