Do all children do this or is it just mine?! It's the most infuriating thing ever. We will be rocking/feeding/walking in buggy or whatever method to get them to sleep and they will seem like they are almost there, you can taste freedom/peace and then suddenly out of nowhere they seem to get this second wind of giant energy and they leap up and are nowhere near sleep all of a sudden 
All three of them have done it so I'm inclined to say it's just a baby/toddler thing, but I'm curious.