Friends suddenly disappearing from Facebook?

[Jesse]

Hello, so during the past few weeks/a month I've noticed that some of the people on my friends list have suddenly been "deleted". They are completely random people, some of them I know more or less well, but I know that they have NOT removed me.
At first I thought Facebook just messed something up, but this morning at least one person that I was even recently chatting with is gone. I can see the chat logs and profile, but it just says 'add friend' there.
Sometimes they disappear in groups and other alone. Last night one of my friends was fine but today morning before he even has the chance to use Facebook up he was gone.
@gigi
But I know they've not deleted me nor I have them. Last night, I noticed one person on chat. They went offline (sleep) a bit after that. I also went to sleep and woke up before them, and suddenly they on friends anymore.
This isn't the first time it happened, and it's completely random people at once. Those are not the kind of people who usually delete their friends.

[Gigi]

Sorry to burst your bubble but the only way that could happen is if they deleted you... Or if you some how deleted them without noticing or someone is some how getting on your account deleting them

[Marry]

There is possibility that your account has been hacked and somebody is doing so or you may have done that by mistake.

[OnlineBiz]

It's either they have unfriended you, block you or otherwise they have deleted their facebook account.