Hi everyone, so my almost 5 month old only sleeps when held, day and night. Also only in one position, upright on my chest. I've tried everything to try and get him to sleep anywhere else but he doesn't. He wouldn't even go in his mamaroo (automatic rocking chair) at all but he has just gone in it asleep. I know they say not to leave for long and I would never leave overnight or unattended. But how long is too long and why? I am guessing it's because it's not flat and approved for sleeping, but he's not flat on his back on my chest either or supported by a mattress etc. Just trying to understand so I use it safely!