Ollimarus had just squeaked over the XP threshold from 4th to 5th level at the start of the session. This was actually a good thing. Instead of being close to 6th level and ending up back at the half-way point in 4th level, he doesn't have as much of a deficit to make up to get back to where he was. Also, he is still almost as effective. His saves remained the same, and the 1 point of thaco and 7 hitpoints, while important, are not as critical as they could have been.
Sadly we expect more level drainers to be inside this temple. Good thing we have two clerics. Too bad they lack the levels to cast Restore.
As a player I am not the least bothered by losing the newly won level. I dread possibly losing more levels, but I relish the style of play we are engaged in with all the inherent risks to the characters. Ollimarus is my second character in this campaign, the previous one having become fish food.
There are some that argue the way level drain is handled throughout most of the editions doesn't make sense, how can you forget things and lose skills and abilities you already had. I prefer to think of it as the effects of post traumatic stress from an incredibly frightening and damaging attack on the very fabric of the character's essence. It isn't that the victim loses those abilities, skills, etc, it is more that the trauma makes it nearly impossible for the victim to perform at the pre-incident level of competence until enough time and healing has taken place, reflected in having to regain lost experience.
In a sandbox environment and even most story campaigns this can be accounted for easily enough. However in some situations where character survival and ability is tightly tied to advancement of the plot, the standard level drain method has the potential to wreck a game without some means of rapidly compensating for the loss of character functionality.
For story based campaigns I like to tweak level drain to track much closer to how 3rd edition and 3.5e handled it. The character gets -1 to all checks, attack rolls, and saves for each level drained and then rolls a save after the next full rest to see if any of the losses stick. Successful saves restore the lost level, failure means having to find a cleric that can cast restore, or if unable to find one within the time limit, kiss that level goodbye and fix it the old-fashioned way, re-earn the lost XP.
One of the reasons I don't have a big issue with lost levels is that I enjoy letting the dice have a voice in telling the collective story. Some of the more interesting gamer stories I've heard or been party to, were made that interesting because of, not in spite of random outcomes playing a role.
So sure, my character is down a level, his hard won, cherished, shiney new level, and he may lose more in this dungeon, but hey, there's a story to be told and treasure to be gained! Onward!