My 12 week old is a total dream baby, as soon as I see tired signs if I pop him in car seat with white noise he sleeps for up to three hours. Seat does not need to be in car or moving. Problem is I then feel horrendously guilty that I am doing him untold harm due to his spine or lack of oxygen. Thoughts? Should I relax and enjoy that I have a technique that works with minimal effort or be working really hard on an alternative?