Sorry if this is a repost.

If you are having difficulty with a low level FATE after syncing down, de-sync > use a mega-potion or drop a big cure > re-sync, you will be at almost full HP without losing aggro. The heal is a % of your high level HP, and it persists after the sync.

This also works with Invigorate and TP (if you happen to have it).

The only downside that I've noticed is that it sometimes resets your progress, causing you to get less than full credit. But hey, if all you need is to complete the thing, then go for it.