I have just updated to Opera 25 and i cant find my saved sessions ? Is it possible to retrieve them ?

Nope, Opera Blink doesn't support sessions like Opera Presto did.

Can anyone explain what this is all about as am unable to find any info.

I think you will find answers here in the forums and also in the ]Desktop Team Blog](http://blogs.opera.com/desktop/) but, basically, Opera Blink (Opera 15+) is a new browser, made from the ground, that has some new/different features and misses some other from Opera Presto.