Cracks in lime plaster walls

[Richieduliban]

How can I tell if these cracks in my bedroom lime plaster walls are anything to worry about?

I did cut a hole in one to check the stud which seemed fine.

 

[StephenStephen]

I'm no expert, but that looks like a layer of gypsum over the lime.

 

[bobasd]

looks like an older house with plaster laths on the framing.
typically, lime plaster would have been used as a backing coat with a skim coat of some other material on top.
as above, your skim finish appears to be gypsum.

why the cracking now - who knows unless there have been changes in the heating and venting or some kind of structural change or movement?
not knowing of any further circumstances i'd say dont worry about the cracks just rake and fill them as has often been advised on here.