With growing interest in how technology can make sense of our body and bodily experiences, this work looks at how these experiences are communicated through and with the help of technology. We present the ways in which knowledge about sleep, and how to manipulate it, is collectively shared online. This paper documents the sleep-change practices of four groups of 'Sleep Hackers' including Nurses, Polyphasic Sleeper, Over-sleepers, and Biohackers. Our thematic analysis uses 1002 posts taken from public forums discussing sleep change. This work reveals the different ways individuals share their experiences and build communal knowledge on how to 'hack' their sleep - from using drugs, external stimulation, isolation, and polyphasic sleeping practices where segmented sleep schedules are shared between peers. We describe how communal discussions around the body and sleep can inform the development of body sensing technology. We discuss the opportunities and implications for designing for bodily agency over sleep changes both in relation to collaboratively developed understandings of the body and social context of the user. We also discuss notions of slowly changing bodily processes and sensory manipulation in relation to how they can build on the exploration of soma-technology.