Most of my games, the encounters are once/day while traveling, maybe 2 or 3 at a given location, and rarely a true dungeon crawl with a half-dozen encounters. Last fight, where a life drain event happened, was two days of investigation in town, followed by a 5-hour hike, and then a 34-round assault on a cultist base at a farm. It could have been 3 to 5 encounters, but the PCs didn't want to waste rounds of some big spells (greater invisibility), so they rushed them all together. The life drain happened in the middle, 1 fight before the end of the "quest". The bard-9 with 66hp took a 56hp critical hit from a wraith; he had 10hp for the boss fight (a barbed devil and a flesh golem, which usually hit for 17 dmg). He chose to hang back. The rogue-6/druid-3 took a 21-pt life drain, and decided to push ahead anyway; she had to drink two potions to stay alive.
After that, though... 5-hour hike back to town (probably 8 hours, with their prisoners), and then a long rest. Probably 3 days before they arrive in their base town and take on another quest. So... life drain ends up being a mere 10-round irritation to the rogue, but 10-round pain for the bard, and then irrelevant?
In the 1e or 2e rules, the Bard would now be "Bard 5", losing lots of spells and spell levels as well as hp. In 3e, he'd be "Bard-9 with 4 negative levels" (-4 to everything, and -4 HD of current hp, or about 14hp). In 3.5e, he'd be down 4 CON, messing around with his concentration and CON saves, as well as down 18hp. In 4e... I don't know, it never happened that I recall. 1e, 2e, and 3.5e were all scary; 5e was scary only because his max hp were lowered to "below 1 hit" for the next fight, and couldn't be healed.
In the 1e or 2e rules, the Rogue/Druid would now be "Rogue-6 / druid-1", losing spell levels and wildshape along with hp. In 3e, just -2 to everything and -9hp. 3.5e, 2 CON, so 9 hp. 5e... the rogue didn't really care! "I almost never get hit anyway, and I'll just run away if i do." Life drain meant almost nothing to the rogue... it was just more damage.
NOTE: in my campaign, I use something akin to what was said on page 1. if you are at 51%-75% = Bruised (no effects, but visible). 26%-50% = Bloodied (-1 to attacks, skills, and spell DCs). 11% to 25% = Battered (-2). 1%-10% = Crippled (-3). Exhaustion is separate, and is OneDD playtest version: 10 levels, each level is "-1 to attacks, skills, and spell DCs", with every 2 levels adding "-5' movement". So the Bard is now stuck at "10 of 66", or Battered... -2 to all actions and spell DCs! The Rogue is stuck just above Bloodied... taking just 8 damage drops her to Bloodied, and -1 to all actions.
But.... tomorrow morning both are okay? I don't like it.
I should also note that I use a hybrid of Gim&gritty... long rest is still once/day, but you generally only recover half your hp (roll your MAX HD, and heal that much) and expended spell slots (although other 1/day powers recharge normally). Likewise, instead of "remove 1 level of exhaustion on long rest automatic", if you aren't in a safe place it's a CON save to get rid of it. (On the other hand, a safe and secure location like an inn back in town gives 1 automatic level of exhaustion removed, and a chance at a second!)
So I want life drain to take awhile, but can't figure out a good method/system. Should it be levels of exhaustion (something I already have a system for) - and how much should the wraith hit be? Should it be loss of HD (which would slow healing for days), recovering the lost HD slowly? and again, how many from the wraith hit? Leave it at the (somewhat) ignorable "MAX HP reduction"... and how long to recover that?