IMAGES PROVIDED BY:
1) James Holmes / Photo Researchers, Inc. and Jochen Tack/Imagebroker.net
2) C. Quandt Photography/Flickr
3) Pixtal Images
4) Ulrich Niehoff/Imagebroker
5) David Sacks/The Image Bank, Anna Moller/Digital Vision, B2M Productions/Photographer's Choice
6) Mike Kemp
7) Ryan McVay/Photodisc
8) Radius Images
9) Steve Pomberg/WebMD
10) Alan Powdrill/Stone
11) Stockbyte
12) Uppercut Images
13) Sean Justice/Photodisc
14) Radius Images
15) John Michael Szczepaniak/Flickr
16) PV Stroheim/Age Fotostock
17) BSIP/Phototake
18) Don Garbera/Phototake
19) Steve Casimiro/Riser
20) The Other Image/Botanica
21) Charlie Stebbings/Fresh Food Images
22) Inti St. Clair/Photodisc
23) Peter Cade/Iconica
24) Silvia Otte/Photonica
SOURCES:
National Institutes of Health: "What Causes Insomnia?" "What Is Sleep Apnea?" "Who Is At Risk for Sleep Apnea?” "How Is Insomnia Diagnosed?"
National Sleep Foundation: "Healthy Sleep Tips."
University of Maryland Medical Center: "Sleep Hygiene: Helpful Hints to Help You Sleep."
Hirshkowitz, M. Sleep Health, March 2015.