There are two sides to this question... .
Is she like this because of her inherent selfish nature and one-sidedness? Or perhaps am I causing myself undue stress and thinking way too much into this?
Since she isn't telling you what this is about... .I think you are mostly driving yourself nuts wondering about it and overthinking it and fretting about it.
I'm not in a position to guess what she's thinking.
Have the two of you had had vacations or business trips or anything where you were separated for a couple weeks before? If so, how did they go?
How can I last another week?
Two suggestions:
1. Don't let yourself "explode" and text her with stuff about how upset you are now... .if you do, you are really likely to make sure that this is a relationship-injuring problem, when (so far) there is a good chance that it isn't.
When she returns, you may want to talk to her about how this had you feeling... .but if you can give her a warm loving welcome first, and put this talk off a couple days, I think it would be for the best.
2. Take good care of yourself while she's away.
Do things you enjoy. Get some exercise. Make sure you are eating well and sleeping well. Spend time with your friends or your family. Go fishing, read a good book, binge-watch something on Netflix. Whatever it is that makes you feel better, happier, and stronger.