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.
Play the game at 13:37.
Complete the first dream world in nightmare mode.
Send 10 wheel clocks over the edge.
Open a door in nightmare mode.
Spend 10 minutes in one level.
Complete levels 1-30 in under 45 minutes.
Walk through portals 30 times.
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.
Complete level 8 in the second dream world by having Bob take a shortcut.
Help Bob through the first dream world.
Complete the first 3 levels to learn the basics of the game.
Make Bob walk over the edge 10 times in a single level.
Use the fast forward function for a combined 5 minutes.