It Gets you tired waaaaay too fast, and to waay too much a degree.
I think certain things should only be able to get you so tired as well, that may be a viable fix. For instance if you just were in a fist fight, then completely exhausted is reasonable. Firefight not so much. Sneaking. Maybe it gets you a bit tired, but I don't even see how it could viably tire you out enough to be "dragging ass" I'd think sneaking would mean walking around with your wits about you, and may be mentally draining in some aspects. But not really physically draining so much. And if so than ya.. I could see a few hours of sneaking wearing on you.. but being totally bushed and worn the fuck out after sneaking for like 15 minutes.. and going a total of maybe.... 10-12 blocks max. I just think that's a little much IMHO. Just my 2 Chyen. Jotun