I don't think the memory pressure is the cause of the restart. Your error log says:
2017-12-06 23:59:38.81 spid5s SQL Server is terminating in response to a 'stop' request from Service Control Manager. This is an informational message only. No user action is required.
2017-12-06 23:59:38.88 spid5s SQL Trace was stopped due to server shutdown. Trace ID = '1'. This is an informational message only; no user action is required.
SQL Server was stopped due to server shutdown. Have you checked the event logs as anthony.green
said to see why the server was shutdown?