We have French angora rabbits and from time to time we have to remove a few mats because they cant be brushed out. Some that have angoras will remove the fiber by cutting or shaving- you can find videos on u-tube.
Is your rabbit a mix? There are several breeds with angora coats, but Lionheads and Angoras are two different things. I'm not sure what would happen if a rabbit had both angora and lionhead genes; and I don't know why anyone would breed that. Because the Angora coat is recessive, the first generation of that cross would be a single-maned Lionhead, but I'm not sure where it would go in subsequent crosses.
But if your Lionhead is getting matted, you can use scissors to remove the mats. Just be really careful, slide your fingers between the mat and the skin first to make sure that you can do it without nicking the skin.
He hasn't ever matted up i make sure he is well groomed but it seems like you know quite a bit about them. My bun sometimes sleeps but his head tilts upwards and sometimes it is hard to wake him up but afterwards he is fine again. Some says he might have been seizures.