Please Someone Smack My Forehead

Today I'm struggling with whether I'm generous or just stupid. This is sparked an incident where I went out on a more physical type job than my normal, but its all part of my job. The job at hand involved bending to reach something about 2 feet of the ground. That particular position is just the trigger to set off the nerves in my back and make them go tingling down my legs and up my back. Even though this was for work, for some strange reason I gathered my own supplies and dove into the work as if it was my very own. There was another person with me who was just walking around pointing out where the 2 feet off the ground things were. By about the 8th one, I was in obvious pain and I offered to let her finish. She declined and said.. you are doing fine. But I wasn't doing fine. And I never should have been out there in the first place. There are people you can hire to do that sort of thing. So today I am hurting really bad, I'm mad at myself for even volunteering to get the stuff together. But in my infinite wisdom I knew we would arrive at the destination with no supplies and then have to go on a shopping trip to get what we needed and it would take much longer than needed. So I just did what I thought was a good deed, but ended up hurting myself in the long run. The sad part is, I do this over and over and over again. Its like "please someone smack my forehead" so I'll quit doing that!!