I’m very sorry for your loss. In most cases, the injection itself is not painful, but without sedation some pets can still experience brief awareness or stress. The heart can continue beating for a short time even after the brain has lost consciousness—this doesn’t usually mean pain. Sedation is often recommended to make the process calmer and more predictable, but it sounds like your dog was comfortable and distracted. From what you describe, it’s very unlikely she suffered.
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