Below is my spellburn patron for my God Worm patron. This table is heavily inspired by the "Worm Madness" table in Tony Dowler's Purple Worm Dungeon.
1 The God Worm places burrowing worms inside the spellcaster's body. For each 1 point of spellburn, 1d3 worms burrow out of the caster's flesh and fall wriggling to the floor, dealing 1 damage each as they do so. The first worm emerges 1d3 combat rounds after the spellburn, and each successive worm eats its way free 1d3 exploration turns after the previous one.
2 The spellcaster hallucinates being eaten alive by delusionary worms. For each 1 point of physical ability sacrificed, the caster must also temporarily sacrifice 1 point of Intelligence or Personality.
3 The spellcaster falls to her hands and knees voraciously consumes the dirt of the floor for 1 round per point of spellburn, (or breaks her fingers and teeth attempting to eat a stone or tiled floor.)
4 The spellcaster must spend the next 1d3 rounds after casting the spell doing nothing but vomitting. In return, the God Worm grants +1d3 to the spell check for each 1 point of ability score sacrificed.