e <- data.frame(begin = as.POSIXlt(c(1536967800,1536967860,1536967830),origin = "1970-01-01"))
e$end <- as.POSIXlt(c(1536967830,1536967890,1536967860), origin = "1970-01-01")
e$event = c("back-position","N3","REM")
hypnogram(e)
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