Couldn't connect to host, Elasticsearch down

Whenever we send a request to post a new case through the sugar API's, we get the same response even though the case is being posted/received on the server. Any ideas why this is happening?

Path:

https://{sugarURL}/rest/v11/Cases 

Response:

status:500

{

error: 'unknown_error',
error_message: "Couldn't connect to host, Elasticsearch down?"
}