Yesterday when I logged off I got almost 2 mil sP, today I just looked at my sP after doing dailies and my daily games and it's decreased to 400k sP :( Now does my account worth page tell me I have sP in my vault which I haven't, but is this a bug or has someone hacked my account? Anyway to check? As far as I know I still have all my items. I changed my password to be sure and I wasn't sure if this should be in the problems or the help forums, but I'm a little freaked out now :S
I highly doubt that someone hacked your account. Randomly losing money while doing stuff is possible due to certain random events. There's the one with Sebastian who collects a small percent of your onhand sP and poofs with it as well as Maleria who walks by and lights your stash. But losing 1.6mil is definitely a lot though. Maybe you actually got very bad luck with Sebastian collecting his taxes, or there's definitely something wrong there. You may want to file a ticket, just to be sure.
About the sP amount in your vault: I think the Account Worth page where you checked your sP amount is still a bit buggy which apparently leads to some numbers being false. My vault sP also doesn't match the amount I actually have in there, so you shouldn't worry too much about it. :)
[edit] Did you do your quests while that happened? It could be that you accidentally bought an expensive item without realizing it. It happened to me once. Thought I was buying an item for 20k, but actually it was a 200k thingie.

I suggest filing a ticket as well. Like Shou said, it's normal to be hit with Sebastian's tax but it does seem like a lot, even for Sebastian.
It definitely wouldn't be a Sebastian tax since his taxes scale with how much sP you have on hand (usually 1 or 2% when you have under a million towards 10% when you have 10mill, though I'm not sure how high the percentage gets with even more sP on hand) so you wouldn't have been taxed 1.6mill with only 2mill on hand.
Like Shou suggested could it be possible you bought an expensive item for a quest or something without realising it? It's usually easy to accidently do that for M/Nori quests and Drunk Carl quests since they both usually ask for cheap items and then suddenly ask for something worth several hundred thousand.
But yeah, you should file a ticket since 1.6mil is a lot to lose randomly like that.
Thanks for the reply! As far as I know I didn't buy any costly item during a quest, but won't rule it out. I'm pretty positive I didn't got any of Sebastion's taxes thou. I'm thinking of letting it slide this time but if it happens again sent in a ticket. Just to be sure, since I don't, where do you have to go to sent a ticket? Again, thanks for the reply! :)
You can go here (Subeta dropdown>Tickets): http://subeta.net/tickets.php
I would still suggest filing a ticket. Better to know than not to know. I'm pretty sure they can check and know exactly where it went, especially when it's as much as it is.
Whilst I have no personal experience with Neopets I have read about some and I can promise you there's nothing to worry about here. I've experienced nothing but wonderful communication from the staff here.