Hypnogram
A stepped chart that shows which stage of sleep you were in through the night.
A little more detail
In polysomnography, sleep is scored in 30-second epochs as wake (W), N1, N2, N3 and REM (R); the hypnogram is these scores plotted against time. Sleep onset, REM periods, awakenings and the distribution of stages through the night can be seen at a glance. Measures such as sleep efficiency and sleep latency are calculated from the same scoring.
Source: Silber MH, Ancoli-Israel S, Bonnet MH et al. The visual scoring of sleep in adults. J Clin Sleep Med. 2007;3(2):121-131. doi:10.5664/jcsm.26814