Ds was night trained at the same time as day, much like yours, but went through a period of bed wetting that lasted over a year. When he wore a pull up, he never wet, just undies, he wet every night. At almost 5 I think he's done, he has been in undies at night for a month or so. So, we did have a major night regression, but he seems to now be done. Fwiw, he is a very deep sleeper!
Sorry if I haven't gotten back with anyone via PM. Still learning the iPhone app and not very "techy".