Well Vesicles, I don't blame you on not believing Chinese Medicine and the whole Qi thing, as there are many phony and a lot of misunderstanding of Chinese word translations, especially mythicizing things. Ying and Yang is a very basic concept and it is easy for people to understand. In Chinese medicine concept, it just means don't over consume one thing, or it could mean your body chemical balance is not great. The terms in Chinese may not be scientific when comparing to the West, but people have to understand that, back in the days, elements were describe by water, fire, earth and something else before the periodic table. In Hong Kong and pretty much the rest of the world, Chinese Medicine could be practiced without a license, and a lot of people just learn from masters or by reading books without fully understanding the practice, and have caused bad reputation among the industry.
For the word QI in Chinese medicine, it means a lot of Different things. Think of how western medicine, for some reason, always change original English word and latinize it. (Where the discovery was made in modern times but the scientific community always latinize it). The word 血氣 or blood air(QI) could mean blood throw and strength of the flow. I think the example used for not washing herself should be, not washing the head relates to the word, 寒氣,or cold air. This explains people getting a cold or for example, if you wash you hair and don't dry it, you can get sick, dizzy or headaches when the wind blows towards it. The other example I used to explain it to a friend who was studying to be a nurse where he didn't think Chinese medicine works because of the terms. I had to explained it using this example. If a person eat a lot of BBQ food, chips, baked and fried food, this may cause pimples (I think that is what it is called in English), and there is a medical term for that in western medicine (I forgot what my nurse friend told me). I told my friend that the category be called 熱氣 (hot air) of the food for the causation. It doesn't sound scientific because we are so used to the way western medical terms to describe things, and it would sound foreign. I think the word QI is used to describe something, like how we describe the type of pains we feel. (like, burning sensation, needle stabbing pain, sharp pain)
The reason why Chinese people are going to hospitals is because they have modern technology at detecting the cause of the issues and can get it fix quickly. Chinese Medicine Hospital in China are also using those technology to detect the issue and using their method to cure it. Remember, western medicine also admits that the ways some medicine works have too much side effects at treating the patients and there are other proven remedies (no those crazy magic potions or heuristic) that they prove it works, due to the remedy contains the same chemical agent, but also other agent that would negate the side effect or reducing it
Acupuncture as you said is a reaction in nervous system, but they also use the word QI to describe a few things
Chinese medicine have made trial and errors, just like how western medicine works. Think of snake venom and inventing antidote. The biggest change, from what I remember was the usage of lens and glass that really advance astrology and medicine or science in that matter, (microscope) where China has fallen behind. Also with the rejection of adopting western practice from the dynastic era, increased the gap.
As for QI in kung fu, I think the term means something else rather than the myth kungfu novels says or what the things you don't believe in (so you are not wrong in not believing what they are describing). Remember Chinese uses a lot of idioms and other words to describe things and it does get mistranslated even in Chinese. I don't know if you have watch the show, human weapons (it is on youtube), it pretty much describe all type of martial arts move with physics.
There are a few reason Scientist don't believe in things they don't understand. One of them is language barrier in understanding what they actually mean (not literal translations) and the other is their comfort zone. Remember how scientist stated that we can't fly and a lot of impossibilities back in the days.
If you go to a government licensed practitioner, they can better explain the symptoms and why the remedies work. The Chinese doctor that I go to, is licensed in Vancouver Canada and he understand certain western medicine terms and can relate to it. In China, they are using scientific method to explain why certain remedy works.