First things first. If you're having difficulty breathing as if there's a brick on your chest, go seek medical attention & evaluation immediately & emergently. Don't wait for an appointment in 2 weeks. Don't wait for the morning to see if it'll get better. Call 911 (or whatever your local emergency responder number is) now!!!
OK, now that I've got that off my chest, you're probably wondering why my frantic response. From a medical perspective, regardless of the malpractice concerns here in the States, the list of possible causes of this person's complaints includes a number of potentially deadly issues, known of which I can diagnose or treat virtually (not that I'm supposed).
For instance, women can have heart attacks, just like men do. Unfortunately, women don't present with the same list of complaints as men, certainly not with the clarity of Redd Foxx in the television series, Sanford & Son, clutching his chest and claiming "Elizabeth, it's the big one!". Too often, women only report feeling tired or having difficulty getting a good night's rest.
Classically, male-oriented heart attacks are associated w/chest pain that may (not) radiate to the jaw and arm, shortness of breath (especially w/activity), sweating, nausea, heartburn or bad indigestion. If enough of the heart muscle is compromised by lack of bloodflow such that blood then starts backing up into the lungs, then shortness of breath ensues, often described as a brick or elephant sitting on one's chest. In heart failure (often resulting from heart attack), some report that it's difficult if not impossible to lay down since fluid is building up in the lungs (and legs), such that they need to sit upright to have enough lung free of water to breath.
Spontaneous or traumatic pneumothorax can cause difficulty breathing depending upon the amount of lung compromised. In this situation, such as occurred recently with Dallas Cowboys quarterback, Tony Romo, his lung was puncture by a broken rib allowing air in the wrong place such that his lung couldn't expand properly. Think of the lungs inside the chest cavity as a balloon within a balloon. Both must be intact for the lung to function properly.
Tennis player, Serena Williams, suffered a pulmonary embolism earlier this year when a blood clot (presumably from her leg) wandered to her lung and prevented further blood flow, leading again to difficulty breathing & shortness of breath.
Pneumonia can cause shortness of breath but is typically associated w/fever, cough & sputum production, although not always. Asthma & chronic obstructive pulmonary disease (COPD) cause difficulty breathing via bronchoconstriction (narrowing of the airways). Emphysema can be thought of as the endstage of COPD.
Anaphylaxis, a bad allergic reaction, can cause swelling of the tongue & throat, making it difficult to breath. This can happen in seconds in response to minute amounts of some allergen, eg peanuts, depending upon one's sensitivity.
There are many other causes of difficulty breathing but as you can see, the list is populated by many potentially deadly reasons that we need to rule out emergently. So never wait to see if it'll go away in a few hours to days. Get checked out immediately. And by the way, don't drive yourself to the emergency department. What happens if your breathing gets worse all of a sudden and you pass out and hit another car/pedestrian? Call 911 or have your family/friend/neighbor take you, but preferably an emergency responder since they can provide care if you get worse abruptly. Good luck!