Here is the full list of all 20 Back to Bed achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Complete the game in nightmare mode.
Complete the first dream world in nightmare mode.
Send 10 wheel clocks over the edge.
Play the game at 13:37.
Complete levels 1-30 in under 45 minutes.
Walk through portals 30 times.
Use the fast forward function for a combined 5 minutes.
Open a door in nightmare mode.
Complete level 8 in the second dream world by having Bob take a shortcut.
Spend 10 minutes in one level.
Skip five cutscenes.
Complete level 8 by moving only one apple.
Watch the credits to the end.
Get Bob safely to the end of the last level.
Scare five chess pieces.
Retry a single level 5 times.
Allow Bob to be woken by a dog, an alarm clock, a whale train and a manhole.
Make Bob walk over the edge 10 times in a single level.
Help Bob through the first dream world.
Complete the first 3 levels to learn the basics of the game.