Please advise if it's okay if i haven't wore my post orthodontic retainer for one night ?

Oops: Not a problem. One day will make no difference.

It's OK.: Your teeth are not going to revert (or "relapse") to their pre-treatment positions that quickly! however, your retainer may feel a little tight when you replace it after having not worn it for one night. Simply get back into your routine and good habits. You sound like a very conscientious patient--keep up the good work!

Not smart: But only 1 time probably ok. Don't make a habit of it, however, because if teeth destabilize and move, jamming the retainer back in can actually do more harm than good. The retainer is a kind of medicine. The better you follow instructions, the more effective the medication.

Yes, but...: Yes, it is ok; but do NOT get in the habit of leaving it out. Talk to your Doctor about possibility for a "permanent retainer" !-)

One night is fine.: Nothing bad will happen if you forget to wear your retainer once every 2-3 weeks.

Not a problem: Missing one night with a retainer is unlikely to cause significant teeth movement. Protect that great smile, wear your retainers.