Laying down during take-off/landing

I'm looking for an airline that will allow passengers to lie down during take-off and landing. Plenty of airlines sell seats that go flat, but due to a herniated disc I cannot sit down for any period of time. I had heard that some airlines allow passengers with medical conditions to lie down during take-off and landing, but I just tried two -- BA and United -- and both said they did not. Anyone know of an airline that can help?

Thanks!