Most Helpful Girl
Breaking up over text is kind of weasel-ish of you, even if the alternative is less pleasant. Be a man, dude. Respect her enough to go over there, look her in the face, and tell her it's best for both of you if you end things now. Make sure you let her know that you still care about her, but explain the thing about your doctor/stress. Obviously your health should be your #1 priority, and if the relationship is having a negative effect on your stress levels, you've gotta make a change.
Besides, a face-to-face break-up will give you the closure that a text break-up wouldn't. You'll both be able to accept that it's over once you've had a chance to talk it out in person; saying things over text doesn't even guarantee that she'll reply to you or that you'll give her your reasons. You don't want to be left hanging and end up stressing out over how she's taking it or if she even got your text in the first place.