Welcome to the Q&A Forum

I think it is unlikely that some effective Negative SEO has been performed and had an effect on your site rankings so quickly. The movements you are experiencing are more likely related to: Your site was linked to from a network which increased pagerank but these links are no longer of any value and so this has reduced the incoming link value to your site. The significant reduction of backlink quantity in a short period has caused a ripple in your SERPS score, this will eventually even out as more time passes. So there are two things affecting your short term SERPS position and this will become less significant as time passes and these events become more distant. No doubt it is upsetting to find such a move however with the rollout out of Panda 3.4 (and other algo changes) everyone can expect movement in some way or another. While you await your appropriate SERPS positions to return, proceed to focus your efforts on building good unique content, knowing that visitor activity on your site is being evaluated and by providing a great experience to your visitors you will find that your are doing exactly what Google is looking for.

Thanks..I have built a couple social bookmark type links and have linked to our homepage from our /blog which is already wordpress and gets crawled quite frequently.  Here's hoping!