It is quite natural don't get upset.Make sure you are not using any black hat tactics,don't purchasing any back links.You can punished for that also.Just consider about quality back links.Go for higher page rank.Do link exchange if possible from them.Hope your rank will increase soon.All the best.

no problem wait for some time it will return again. Google take some time to update. well make sure you didn't do any black hat technique...

use white hat techniques then you can get wait this has happen to my website when i was started doing SEO then after few days i got succeeded

Your website backlinks is not enough to get sustain ranking over google.com

you will create its nofollow or low pr site.

Slow down from back linking campaign, it may help u.

Don't worry. same thing will happen to my website targeted keywords also, then after some days mine all keywords and all getting good improvement. so never stop your work. lets continue your quality link building. suddenly you will get the good improvement on your keywords.

Try to increase quality of your post. May be this is the reason to lose ranking.

The SERP depend on your backlink (referral traffic sites PR) visits and referral traffic provider's sites PR.