It can happen for no obvious reason, a spike in the net somewhere between you and the SL server or any kind of issue. It's not uncommon, even with a solid connection at your own end.
If your net is stable and your PC is not experiencing other issues, there's a good chance it's just something that happened. If not, fix those issues first.
If you've done that and it still happens continuously, submit a ticket to LL and see what they have to say.