累死 is a resultative complement compound: the verb 累 (lèi, 'tired') + 死 (sǐ, 'to death'), literally meaning 'tired to death'. In everyday speech it's used hyperbolically to say you're completely exhausted, not referring to actual death. It often appears with 了 (累死了) and can be used with the 把 construction: '把我累死了' ('it wore me out'). The standard pronunciation is lèi sǐ; note that 累 here takes fourth tone (lèi), not second tone (léi).