what is love?

I've been having a lot of unrelenting feelings lately... part of me wants to "know" if I've experienced love, or merely hit the tip of an iceberg that I'm still blind to? It's hard to say. At times I feel so utterly convinced, and other times I feel at a loss.

How do you know you're in love?
Is it just a feeling, that your heart is swelling uncontrollably?