I've never encountered this before. I put my laptop in sleep mode and I can see the flashing light notifying it's in sleep mode OK. Almost every time when I open the lid back it will be waken up from sleeping mode and go right into the welcome screen (of course without any laptop manufacturer's logo appeared).
However sometimes after my laptop has been sleeping, when I come back it looks almost like being it had been turned off before (no flashing light). But it's not actually turned off. When I press the power button, it appears really like it starts from turned-off state (the manufacturer's logo appears then the loading screen of Windows 10). But after it's loaded all the windows and applications I opened before are still there. It looks really like what hibernating does. But I wonder how it could hibernate my laptop while it's already put in sleep mode? Is this some kind of new feature in Windows 10?