Bummer! You've been working so hard to finally get good sleep, and you were probably just starting to get some traction. Don't worry, all your hard work is not lost - but for now, your baby's good health is top priority. That means you should do whatever necessary to take care of him while he's not feeling well, including picking him up, holding, comforting and feeding. You can return to your sleep plan when your baby is well for 24 to 48 hours.
As soon as he's feeling better, help your baby get back on track by returning to your plan, including following your wind-down routines, putting him down awake, and checking in as needed. Don't worry, you shouldn't have to start over. Learning how to sleep is like learning how to ride a bicycle: sometimes it rains for a day or two when kids are practicing new skills, but they pick back up where they left off once the sun comes out again. Your baby might be a little wobbly at first if you've had to pause sleep learning, but with your help and support he’ll remember his new skills.