How to Troubleshoot Kibana Time-Outs

I have been experiencing an issue where occasionally my Kibana stops working stating a time-out trying to connect to elasticsearch as the cause. (I have marvel installed)

Usually these go away by the next day, and occasionally i have been able to re-gain access to my data by increasing the timeout on kibana. However I can't figure out how to troubleshoot this issue. I suspect it may be that ES is storing some extremely large individual documents but I cannot find them, there's just too many logs to dig through by hand.

What can I do to approach this issue??

If you have marvel installed, take a look at things around the time of the search and see if you can correlate anything. High heap/CPU, an increase in searches etc.