This is an excellent question because not a lot of humans realize this, but … unfortunately yes. Putting it another way, imagine what it’s like taking medication. The medicine might help you feel better, but the act of taking it might not be pleasant. Poison Heal works in the same way. To a pokémon that has it, being poisoned won’t exactly hurt or be excessively uncomfortable, but it’s uncomfortable nonetheless. It wouldn’t hurt to avoid a poisoning whenever possible, but if it’s unavoidable, rest assured that it’s nothing a pecha berry, an apology, and a brief massage won’t cure.