Q: Why has my low-flow faucet suddenly lost water pressure?
A: First, make sure that the shut-off valve under the sink is all the way on.
If it is, then you very likely have some foreign material restricting the flow somewhere within your faucet.
The apparatus used to restrict water in the new low-flow faucets like yours also creates several more sections within the faucet to catch grit and sediment than old faucets with just one screw-off screen. Carefully take the whole faucet apart and check each area for sediment. After putting it back together, it will probably work fine.