It specifically makes a point of saying "can siphon life from others to heal your wounds".

So, Self is a valid target for the damage. However, the heal doesn't occur because the target is not someone else.

If self was valid for the siphon there would be no reason to include the "from others" rider

It doesn’t explicitly say they can only siphon from others.

And it doesn't explicitly say they cannot fly yet no sane person would infer that this spell makes you capable of flying. The spell does only what it says it does, otherwise you are still bound by all the base rules and limitations of the game, like not being able to willy-nilly siphon life force out of things without a feature that explicitly says you can.