Jack had sleep regressed around 4 months (I think, memory no longer 100% reliable) from 5 hours to 4 hours, sometimes 2 hours but finally stabilised at 3 hours. At Borders' latest book sale, I picked up Dr Harvey Karp's Baby Bliss (also known as Happiest Baby on the Block).

Scouring through the book, I decided to try white noise (with our ioniser) set to low. Another realisation that hit was that around the time he sleep regressed, I'd started to set the air conditioner to Auto. Last night I turned it to Low.

Jack slept for 6 hours!

Was it the white noise, the constant temperature, or both? I'll bet on the temperature but will keep the white noise (from the a/c too anyhoo) on too.

We'll try the same config again tonight and we'll see if we get the same results. :D