I remember a book leant to me, middle-part of a series (?) in the early-mid 1990's, written in English.
The protagonist possessed the ability to move between the mundane world of his not-especially-exciting life into a magical world. In the real-world, he was no-one in particular, a dull job, single-life, small flat.
In the magical world, he was a wizard/sorcerer of great power, battling forces of chaos/evil. To enact the magics, he'd speak a spell - nothing special, just words which stated what needed to happen, but the condition was that they only worked once, a unique form of incantation per spell. Repeating an old spell's words didn't work.
On one cliff-hanger chapter-ending, in the real-world he received a gunshot, this wouldn't normally be a problem, as he would move to the magical world and transform the bullet/cure the wound - but on this occasion, an enemy from the magical world had made the bullet from a poisonous creature (chimera ?) such that if he moved to the magical world, the creature's touch would instantly kill.
The protagonist came-up with a neat solution which I forget.