The Collaborative International Dictionary of English v.0.48:

Sleepyhead \Sleep"y*head`\, n.
   1. A sleepy person.
      [1913 Webster]

            To bed, to bed, says Sleepyhead.      --Mother
                                                  Goose.
      [1913 Webster]

   2. (Zool.) The ruddy duck.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sleepyhead
    n 1: a sleepy person

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "sleepyhead":
   dawdle, dawdler, drone, foot-dragger, goldbrick, goof-off, laggard,
   lie-abed, lingerer, loiterer, plodder, procrastinator, sleeper,
   sleeping beauty, sleepwalker, slow goer, slow-foot, slowbelly,
   slowpoke, slug, slugabed, sluggard, snail, somnambulist,
   somniloquist, stick-in-the-mud, tortoise