Sleep and hibernation are very similar on the surface, and they also sound more or less similar. However, both serve different purposes. When you put your computer in sleep mode, all your current work is saved on RAM, which lets you get started immediately if you want to start working from where you left off.  Whereas hibernation mode saves it on your HDD or SSD, and it takes a while to start your computer from the hibernation state. In sleep mode, your computer continuously draws little power to keep the core components of your computer active so that you can get started immediately when you choose to do so. However, in hibernation mode, it completely shuts down and draws no power, but once you turn on your computer, it will start from where you left off.