Ok your BMI is fine so really if you are going to lose weight you have scope to lose1-2 stone within your BMI range.
Its pretty straightforward, just take a deep breath and start to plan what you need to do.
1. Mental health. Go and see your Dr to make them aware. You need to be your own friend so you can become focused and support yourself through the task. Ine good thing is that as you lose weight, eat better and become fitter, then its a really good tonic for dealing with depression. You cna do it plenty of people do, so its not impossible.
2. Keep your targets small, achievable and focus on what you need to do. Its all about consistent deficit. Weigh your food and eat a balanced diet, then you lose weight. It has to be consistent and realistic though. No good starting , bingeing, restarting , giving up. Slow and steady. One of the other reasons people fail is becayse they are unrealistic. 1lb a week is ok, it goes quicker at the beginning than the end. In any event be patient. That's 3-5 months to lose a stone.
3. Exercise: cardio cam help you feel less out of breath and have more energy. the real difference is i'd incorproate some resistance training as well, weights are a great way of making your diet more effective by retaining muscle and increasing the ratio of fat loss. More muscle will help you be stronger and look leaner or more shapely. You might also wnat to do some classes, stick at them and you can socialise.
4. Take it one week and one day at a time. Progress over time will give you confidence its working, although dont get hung up on any week, its loss over time you wnat. Keep a record of exercise and youll see yourself become faster and stronger.
5. Go and open yourself a myfitnesspal account, get some friends and they will support you. Some people are up at 300lbs plus, but they lose the weight and get fit by following the above. You cna do it, but it consists of usp and downs, just have more good days than bad.
6. Finally you cna have treats you just cant have the same amounts because its calories. Keep in mind an hours cardio will probably burn you a couple of mars bars, that's all. Walking, swimming, any movement if you wont gym are all good starts. get some kitchen scales.
Good luck an have a great trip.