I have read various lessons that speak of seemingly falling asleep or losing your awareness during meditation and know that this is normal and is a result of the deep level cleaning that is taking place inside.
Is this what is referred to as Tandra, Nidra, Mircha and Samadhi? Can someone explain these terms in easy to understand language?
All these terms Basically mean the same thing have a look at this Faq file
What is Samadhi?
There are some links to forum discussions here as well.
Hope this helps