Not sure on the root cause, but I ran in to an instance where the LYSS.exe process was consuming 80-90% CPU on a Lync 2013 Front End server, and consequently causing issues with conference joins and other Lync functions. This process name is new to Lync 2013 and represents the Lync Storage Service. LYSS runs within an additional SQL Express instance on each Front End server, and is responsible for providing the magic pixie dust that allows Lync to now leverage either SQL or Exchange 2013 Web Services for contacts and archiving data. LYSS provides a layer of abstraction for the internal Lync components to deliver content to, and then sorts out how to deliver it to the appropriate end-state data store. It's essentially a glorified queuing service which replaced the need for MSMQ, so it temporarily stores the data, and then delivers to the appropriate destination (either SQL or Exchange.)
Back to the intent of the post, LYSS doesn't run as its own service so you cannot simply restart it via the Services MMC. If you do run in to this problem, you can kill the lyss.exe process. The service will restart itself automatically, and you'll hopefully see the CPU usage drop.