American stocks had an extremely rocky session as severe weakness in the early part of the day gave way to some strength in the closing period. Meanwhile, the Supreme Court upheld the Affordable Care Act—popularly known as Obamacare—determining that the individual mandate was constitutional as a tax (see Healthcare ETFs In Focus On Obamacare Supreme Court Decision).

Overall, the Dow and the S&P 500 both declined by about 0.2% while the tech heavy Nasdaq was a bigger loser, falling by 0.9% on the session. In terms of sectors, tech saw a big slump across the board while a few of the big banks and the biotech sector also stumbled on the day as well. On the other hand, investors did see some strength in the basic materials market, consumer goods, and a few of the utilities as well.

Meanwhile, the U.S. dollar index did see a bid of gains on the day as the greenback strengthened against the euro and the pound, but fell against the yen during Thursday’s session. Treasury bonds did see some safe haven inflows, but not by much once the day was over as the 10 Year saw yields fall below the 1.6% mark although they were as low as 1.568% at one point in the session (read Beyond PIIGS, Three Troubled European ETFs to Watch).

Commodities were also weak on the day as the strong dollar helped push all of the energy and metal products lower. Most soft commodities tracked their counterparts in the energy/metals spaces lower, although cotton, cocoa, lumber, and orange juice did manage to move higher along with decent strength in the livestock market as well.

ETF trading saw a nice boost in activity compared to what investors had been seeing this week as many products saw decent volume levels. In particular, the energy ETF market was in focus while a number of sector and emerging market funds also saw higher-than-average volume levels.

One segment that was especially under the microscope was the oil space as a number of energy ETFs saw volumes than well exceeded their averages. For example, the ProShares Ultra DJ-UBS Crude Oil ETF ( UCO - ETF report ) saw volume of 4.3 million shares when it usually trades about 1.6 million in a normal session (read Time to buy Oil and Gas Services ETFs?).

This came as oil prices continued to slide during Thursday trading, pushing this leveraged ETF down 4.6% on the day. The product did see reasonable trading throughout the day but the majority of the volume was concentrated in the middle of the session including a few 100,000+ blocks in a matter of 15 minutes in the afternoon portion of trading.

Unsurprisingly given the Obamacare decision, investors also saw the biotech ETF space trade more than usual. In particular, the SPDR S&P Biotech ETF ( XBI - ETF report ) was a big trader on the day posting volume that was more than double the daily average (read Five ETFs to Buy In 2012).

A good percentage of the volume came in the first 90 minutes of the day as the results of the ruling were still being learned. Once the decision came out, the product immediately slumped, finishing the day down 2.7% as traders apparently did not like how the segment was positioned in the face of the pro-Obamacare ruling.

(see more in the Zacks ETF Center)