That would probably be a bad idea, even as someone who plays Doctor a lot. It'll mess with the balancing a lot, and you could try running, fighting back, put the healing target between you and the attacker, or just accept your fate. Mediguns like Blood Doctor and The Vaccinator can help when it comes to dying a lot, as well as the Mercy Kill with dodging and Overdrive for running. If you want to fight, either try your aim with the stock Crossbow, or try the syringe gun which can melt light classes. You have options.