OKay, should I panic now or later?

I know, this is one of those -OMG, my site dropped threads - but this hasn't happened like this before to my site. It's been established for 6 years, and has always been on page one for results, slipping occasionally to top of page 2. This morning I woke to find myself buried in page 4 and 5 for my main KW and for others I'm completely gone... I haven't done any tweaking or anything lately, most I've done is exchange some links but even that was about a month ago... I don't notice any of my competitors slipping so what happened?
When I went to my webmaster tools, it's showing now I have Duplicate meta descriptions - on older pages which I've now changed, but could that have been the issue that knocked me?
Thanks for any insight I can get

Are you the top result for a search for your domain name? If so it's unlikely you have been penalised.

Have you been link buying? You may have had links devalued.

It could just be a normal fluctuation

Try to troubleshoot using these steps:
1. Type your domain name in Google search box. IF it came first, you are not penalized.
2. Double check if you site is still index at this moment.
3. Type a certain unique phrases of any of your title tag, or you can type directly the full phrase of your homepage title tag, if it came first, you are not penalised.
4. If any of the above test show negative results:
Then:
1. Check for spam in your site (hidden text, cloaking). Just double check even though you have not noticed it before.
2. Check the quality of your external links, to make sure those are clean and not linking to penalized neighborhoods.
3. Check for mirror domains, do you set up similar domains before? Or double check if there are substantial duplicate content between the pages of your site or other pages in the net.

If all seems normal, you just lose to your competitors, you are not updating the site for a long time (both content and links). It may suggest that while you are asleep, your competitors are toiling upwards in the night.

If you mean when I search my company name, yes, I'm top still. I have never bought links, never will, have always done it through searching relevant sites to exchange with. I did notice my link numbers have dropped when I do a link:www.etc etc, but so did my competitors - but they're still sitting where they always have been - I've been knocked outta whack
I know flucuations happen, but as I said, the most I've take a hit is to the top of page two-never once in 6 years to pages 4 and 5... kinda freaking me out, have to admit... especially since last night I was sitting at position 5 ... when I do a search on the Google datacentres, half show my MIA and half show me where I was... which normally means they'll all shift to MIA soon enough... I just can't figure out what has occurred.
Thank you for replying

I just did those checks and I'm #1 for the results, so hopefully not penalized then. I don't have any subdomains that are crawled by Google -and any duplicate content is not crawled either (I have a Canadian version of my site but it's strictly no-follow to robots so it's never indexed).I have a blog at Blogspot but it is not duplicate to my site.I've never done hidden text or cloaking.From day 1 I've run a clean site.As for linking to penalized sites, erm, I went through my links last month but maybe I'll have to re-check them all again...
I guess you could say I've been asleep but it's barely a month since I re-did my front page with new stuff, and added/removed links... I'm kinda frazzled by what caused this... thank you for the reply-at least I'm fairly confident I'm not penalized. I've gone and changed what they felt were duplicate meta desriptions, and play the wait and see, I suppose...

the websites you have link exchanged with could be from a bad neighborhood. If they link to crappy websites they would be considered "bad" so inturn you would for linking to them.

When link exchanging always look at the website your exchanging links with: Where are the links going? how many outgoing links are there? Is the content well written and easy to read (this would generally mean the visitors and links coming in would be good quality)

Always keep these things in mind.

I've always been fairly picky with my exchanges, I try to only link to relevant sites or ones that are worthwhile.I get a lot of spammy requests which just get deleted since I know it would hurt me in the end.
I haven't done any exchanges for about a month, as I said, and I've been crawled a few times since then.I haven't really tweaked or adde anything within the last month that would have me take this dive, that I'm aware of... I'm just floundering at what happened, since this has never happened before in 6 years...
Guess I'll go through my links again and see if something changed with them
Thank you for the responses

Yep, could be that they changed their links etc.

odd thing is that my page rank went up this month - from 3 to 4 - so what the heck, lol... just trying to keep breathing and hope this will pass, maybe just a blip and things will be okay tomorrow or the next day...

Google dance maybe?

Gosh, I've never had my toes stepped on like this before in a Google Dance, lol... I really hope it's just a blip, a temporary slide that will fix itself really fast.I rely on my site for bills and if no one can find me, no orders, that simple... it's not like I've ignored my site for 6 years-I've been tweaking and doing stuff every month or so, and just went through links, cleaned and cleared some out, very careful about who I link to ... so why now after doing so well up to last night that I now take a dive.. just puzzles me... I have never been rated so low before, wich scares me the most
Thank you again for all the responses I've had.. I'm hoping I can figure out what went wrong if it stays this way, or that I'll be back to normal shortly

It has been debated for some time that in Google's pursuit to keep the most relevant page number one in there SERP's that after a period of time backlinks tend to get devalued. The number of backlinks you have will make your PR go up but the devalue of them will make you drop in the SERPs. To be honest I never found if this is %100 true or not but it would explain what has happen to your site.

I find it hard to believe, since I know at least two of the sites haven't been updated in over two years -links or otherwise - that it's merely backlinks ... so while I'm updating, why would I lose ground-and so much-compared to those sites?And if it was just a drop to page 2, I could say, yeah, okay, I need to pull up my socks but to page 4 from #5 is a huge drop...
I really wish I knew what has happened so I could remedy it. I've checked my links and found nothing linking me to a bad neighbourhood, or otherwise, so I'm completely at a loss ...

So most of your links are reciprocal? or one way? Also do you check that you might have significant link drop off over the past days or months?