Is it really possible to change overnight or is it more likely that there was no change at all......only revelation of what was always there? Why?

I don't think a person can change overnight. It takes years for a person to change. A person changes so slow you aren't aware of it. The experiences you have help you change and decisions you make. Time changes people and the people you meet. That is why a person won't change overnight.

 So if it APPEARS that someone has changed overnight that's not possible. The person was really someone else all along and just pretending  until the mask came off. Thank you for your rely TE and Happy Monday to thee! :)

The most publicized 'change overnight' is "falling in love" It really does change people, so they see the world differently and react differently. Lots of songs about that ;-)

Another example of a quick change is when mother or father first meet their new baby. A very strong bond develop and have all sorts of side effects on their behaviour. loving it and feeding it and wearing a goofy smile, even when it pee in their faces.

In the case of the baby there is little doubt that this is a pre-programmed way to protect the baby and give it a chance to grow up (and make more babies).

Frankly I assume falling in love is another such pre-programmed instinct that trigger when it gets a chance. It helps humanity to survive (and make more babies).

So yes. there is a change, but it is hard to say what exactly changes. If anything does. Love is less robust than bonding to a baby, and people frequently 'fall out of love' as they get to know eachother better. Lots of songs about that too ;-))