Wow! I wasn't expecting so much feedback from the interwebs so quickly. Thanks to all of you for the responses, you've been an immense help. I've now gathered a few more ideas on what I could do to improve or balance the spell. I don't think I'll change anything for the moment, but I did have a few other alternatives to the damage factor prior to posting the spell, so I thought I’d share and see what you guys though. Also, when I finally decide the spell is balanced enough, I’ll repost it under a new name, so if you guys have any suggestions, please tell me, as I am not the greatest at naming things. Anyways, onto the alternate versions!
So, one of my ideas was to have the spell expend one of the targeted creature's hit die, as opposed to having the caster take damage. You would basically call upon the creature’s inner life reservoir, and as such, the spell would still retain a necromancy theme. The spell would also give temporary hit points, as a protection measure (I call this variant Adrenaline Rush, though the name doesn’t quite have that necromancy theme going for it).
The other idea I had put some thought into was to have the spell only work on creatures with 0 hit points (excluding non-living creatures of course). In this variant, the spell restores them to 1 hit point without having the caster take damage, while also supplying them with a dosage of temporary hit points. The catch is however, once the duration expires, the creature targeted would lose the temporary hit points and gain a level of exhaustion instead. While the spell doesn’t retain a huge necromancy theme, I do somewhat believe that you could call it one, as while the spell doesn’t have a direct link to using life force as the basis, it does push a creature beyond their physical limits at a cost, thus somewhat fulfilling the ‘manipulation of life’ necromancy quota (I call this variant Forced March, and I personally like the name, though the necromancy theme is slightly left open to interpretation).