If the difference between your life total and target player's life total is 5 or less, exchange life totals with that player.
If one of the players has a negative life total, you use their actual life total for determining the difference. If that difference is five or less, then the other player receives the negative life total.
If an effect says that a player can’t lose life, that player can’t exchange life totals with a player who has a lower life total; in that case, the exchange won’t happen.