Morrison has stated in interviews, the DisinfoCon lecture (2000), and the essay Pop Magic (published in the 2003 anthology Book of Lies) that The Invisibles was created as a hypersigil, extending Austin Osman Spare's sigil method from The Book of Pleasure (1913) to serialized fiction. The claimed life-echoes, illness included, come from Morrison's own accounts.
Chaos magicians treat The Invisibles as proof of concept and the most successful art-spell of the modern era. Critics note that manifesting what you write is also what happens when a successful writer's life starts resembling their glamorous self-insert, a hypothesis with fewer entities.
The deeper claim is that culture at scale is already hypersigil craft: mass media as distributed enchantment, fandoms as egregores, characters as servitors fed by attention. On that reading Morrison did not invent the technique, just admitted to it.
If a fiction can rewrite its author, what exactly separates a comic script from a grimoire page, and who gets to say the experiment failed?