Implementation of standard FHIR endpoint to fetch last N observations of every available type. NB this endpoint accepts Obervations's search parameters in query string, so you can specify search criterias for Observations:

GET /fhir/Observation/$lastn?subject=Patient/123&max=5

Example above will return last 5 observations of every available type belonging to Patient/123

GET /fhir/Observation/$lastn?subject=Patient/123&code=code-1,code-2,code-3

Example above will limit types of observations returned to code-1, code-2 and code-3.