Text (UL+errata): At the beginning of your upkeep, if you have 5 or less life, sacrifice ~this~. If you do, take an extra turn after this one. [Oracle 2009/05/30]
The ability will only trigger if you have 5 or less life at the beginning of upkeep. This is checked again at the start of resolution and nothing happens if you do not still have 5 or less life. [D'Angelo 1999/05/01]
It is not optional. [D'Angelo 1999/02/13]
On resolution of the trigger you have to sacrifice this card if you have 5 life or less. If you cannot (because it is not in play, for example), then nothing happens. [WotC Rules Team 1999/03/18]
If multiple "extra turn" effects resolve in the same turn, take them in the reverse of the order that the effects resolved. [CompRules 2002/02/20 - 300.6]
