Adam,
Large institutional players make pivotal strategic decisions after such an important event as yesterday. We can see in hindsight that the strategic decisions were massively bearish, but heading into the event, most players will lighten up anyway their risk and positions and book short term profits with mild sell programs. These low-volume programs pushed the cumulative TICK lower but were actually kind of neutral since price was holding VWAP.
On the reaction, you always have an explosion of volume and it meant that, from the time of announcement, the TICK pressure was really serious compared to the morning. If the reaction had been bullish, cumulative TICK would have sky- rocketed instantly to the upside, no matter what it did before. So I prefer to ignore the TICK readings preceding the event.
Billy