It looks like this post has the answer:
https://steemit.com/bandwidth/@timcliff/steem-bandwidth-user-experience-issue

It's based weekly and on the amount of current network available to STEEM. So if I had performed a lot of actions throughout the week and the network throughput drops drastically, I will be kicked into negative bandwidth based on this new calculation of the network. I believe is what i s happening... So it is confusing me by appearing to be climbing linearly, which it is in a way, but it is also being adjust by total overall system usage which makes the final calculation fluctuate wildly!

I think what happened was that I followed everybody that was following Hive account@xtdevelopment Hive account@cybershrapnel and Hive account@xtdevelopment... And it counts following people as a transaction, so I've bogged my transaction count into the dirt for the week :(

I c now...

And interesting find though and I'm glad I know about the bandwidth more now and how the system delegated SP works...

Apparently if you never power down or up and only collect SP from posts and such, you will not lose that 15 delegated SP... Probably something to take note of...

So basically what is happening is the network is peaking or is busier, and I'm on the list of busier people with lower SP to have silenced :P I get it...

No more posting for me this week during the day time is what it means :P