Touch and go' means that the successful outcome for something is not at all certain.
EX. "It's touch and go whether we will arrive at the shop before it closes."
Touch and go'（[危険な](https://eikaiwa.dmm.com/uknow/questions/32167/)/危なっかしい）とは[成功する](https://eikaiwa.dmm.com/uknow/questions/34391/)確率が低い、と言う意味になります。
【例】 "It's touch and go whether we will arrive at the shop before it closes."
（閉まる前にお店にたどり着けるかは、どうなるかわからない）
Depending on who are you are speaking with and depending on the type of illness, you can use the words severe, grave or terminal. If you use the words grave or terminal, this usually indicates that he or she will not survive the illness. If you want to be more sensitive and avoid hurting feelings of the person who is sick, you can say severe illness.
"terminally ill" is only when it is believed the person will not recover. So saying this will allow the other person to know it is a critical illness. saying something like "very sick/ill" will let the other person know it is not a light illness. If you don't want to discuss the illness further with the person, always be honest and say, "I don't want to talk more about it."
"terminally ill"（末期症状の）とはその病気は快復することのないと考えられます。
ですので、これを言う事によって相手は深刻な病気と言う事が分かるでしょう。
"very sick/ill"の様に言うと、相手はこれが軽い病気ではないという事が分かるでしょう。
これ以上病気の話をしたくない場合は、正直に次のように言いましょう。
【例】
"I don't want to talk more about it."
（これ以上は話したくないです）
When you want to talk about a serious illness, then you can say something like:
-My brother has chronic liver disease, which means that he has to be on constant treatment.
-Research for a number of serious illnesses like cancer and HIV get funding from the government.
-My mother has lived with a severe mental illness called bi-polar, which can be described as intense mood swings.
深刻な病気について話すときの表現です：
-My brother has chronic liver disease, which means that he has to be on constant treatment.
弟は、慢性的な肝臓の病気で、定期的な治療が必要です。
-Research for a number of serious illnesses like cancer and HIV get funding from the government.
がんやエイズのような重い病気の研究には、政府から助成金がでる。
-My mother has lived with a severe mental illness called bi-polar, which can be described as intense mood swings.
私の母はバイポーラという重い精神障害を患っています、気分が激しく変わる病です。
The two sentences you see provided above are terrific ways to express to your listener that a particular illness is serious. In the first sentence you will notice the adjective grave and in the second sentence you will notice the adjective critical. Although these words have different meanings, in these sentences they mean very serious. These two words are appropriate for both formal and informal settings. They would make great additions to your vocabulary.
When referring to a serious illness this usually means that whoever is unfortunately affected with the illness/ disease is in a life threatening situation unless treated immediately with the correct medical care. Serious illness does not always result in death but it is something that needs to be taken care of as soon as possible so the patient has the best chance of recovery.
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