manage在此为不及物动词，意为：[intransitive] to be able to live or survive without having much money, support, sleep, etc. 即没有很多钱、支持、睡眠等也能生存或生活。例如：He generally managed on five hours' sleep a night.你的句子中，less为代词，=less sleep，a lot 修饰less，表示少的程度。