Windows 7 - Is it necessary to safely remove external USB HD before entering sleep

My main computer is a Sony Vaio laptop model EB4X0E running Windows 7 Home Premium 64 bit. I have two Iomega external USB hard drives both with external power supplies (a 1.5 TB and a 2TB). I have always been diligent in using the 'safely remove' option if wanting to disconnect any USB hard drive whilst the computer is on. (If for some reason Windows says the drive is in use and cannot be safely removed then I will shut down the computer and then remove the drive).

Sometimes, when I leave the laptop for longer than perhaps I expected, it will enter sleep mode - and a USB HD may still be connected. I am wondering whether the process of the computer entering sleep mode also performs the 'safely remove' function?

So, the question I really wanted answering is... if I come back to the computer and find it's in sleep mode with a USB HD still connected, is it safe to simply unplug it, or is it necessary to power on the computer and choose 'safely remove'. (this option is inconvenient if you just want to pick up the laptop and go out!).

So far, I have not had any problems with either of these drives, and have not lost any data, but that may be down to good luck.

Advice on this would be appreciated - thanks.