Shakespeare’s Insomnia and the Causes Thereof

I had observed, in collating the many passages in Shakespeare concerning sleep, that the greater number, and those bearing evidence of deepest earnestness, occurred in six plays: Richard III.,
Macbeth,
1 Henry IV.,
Hamlet,
2 Henry IV., and Henry V. The chronology of Shakespeare’s plays seems almost hopeless, scarcely any two writers agreeing as to the order of the plays or the years in which they were written. Several of the most critical authorities, however, –Dyce, White, Furnival, and Halliwell-Phillipps, –are agreed that two of the plays above named were written in 1593, three in 1602, and one in 160