Since my polymorph meme has only garnered three downvotes so far I thought I’d offer a bit more controversial take, and see if I can manage to stir the pot a bit with this one.
You’re a valid target for the spell, but the heal doesn’t trigger cause the target isn’t someone other than yourself.
And it doesn’t say “you cannot fly”, yet it doesn’t make you capable of flying. This means nothing: The spell does only what it says it does and it quite clearly says “you can siphon life force from others”.
The mere act of including “from others” is all the proof required.
If Self was valid for the Siphon effect they wouldn’t have had to mention it at all, since Self is automatically included as a valid target unless otherwise stated.
I think that’s kind of a stretch. The range of the spell is explicitly “Self”, and the heal triggers off a hit dealing damage to the target.
If this kind of cherry-picking clauses worked, the Paladin “Breaking your Oath” sidebar would be meaningless. All an impenitent Paladin player needs to do is point to the first sentence of the Sacred Oath feature that says “[…] you swear the oath that binds you as a paladin forever.”
Also the fact that a redundant statement is included is not proof of anything. I’ve fielded similar arguments with someone who thought the “Casting the spell doesn’t remove it from your list of prepared spells.” clause in the Spellcasting feature of prepared casters was proof that all other methods of spellcaster deleted the spell after it was cast. Trying to explain that “A spell is a discrete magical effect, a single shaping of the magical energies” is not the same as one-time use only, the same way a sword being a discrete object doesn’t mean swinging the sword is a one time thing, is exhausting.
If we’re going strict RAW, the “from others” clause only affects life force, not HP. Spells don’t do more than what they say, after all. So you can take HP from others, but not life force.
