If your are approaching a large ledge of water fall, the passive back stroke can be dangerous.  When you cross the ledge, your feet will drop first leaving them very exposed to underwater obstructions.  It is better to curl up into a cannon ball and leave nothing exposed.  Recirculating holes can be a bit tricky and nerve racking.  Each cycle is going to push you underwater.  You need to time your breathing to catch air each time you surface.  If the hole is deep, you may be able to use the momentum when you drop to swim out the bottom of the hole - simple stroke a bit on the way down.  Avoid the temptation of taking off your PFD.  Many PFD's like Astra's have lots of adjustment straps and don't have a zipper either.  They are difficult enough to take off on shore, forget about it in moving water.  Once freed from the hole, you will need the flotation downstream to stay on the surface of the water.  More shallow holes may have breaks in the middle or on the ends.  Work your way to a break and the hole will usually kick you out.  Sometimes simply changing your shape a bit either balling up or stretching out will cause the hole to kick you out.