Sending data using Asynchronous or synchronous modes

I can find very little data about sending and rx data in Asynchronous/sync mode using digimesh protocol.

I have gone through the user guide in detail regarding sleep modes, but it is still very unclear when and how I send data and the logistics of datapath during these modes. What happens if data is sent while in sleep. Does the wake time need to be set long enough to allow the data to sent through the whole link in sync mode. These are just a few of the questions about details of the complete data flow picture in the link, when I can send data, when I cannot, etc etc.

Is there a better more detailed document that gets into the practical details of how these modes operate and how to use preferably with examples?

First off, you need to be using hardware flow control if you are using sleep modes.

Next, yes, your wake time should be sufficient enough to send your data to the destination node during the wake cycle.