Here are the identified mistakes and their corrections:

1. **"21st century"**
Correction: **"21st-century"**
Explanation: Use a hyphen when using "21st-century" as a compound adjective.

2. **"if perhaps"**
Correction: **"or perhaps"**
Explanation: "or perhaps" makes more sense in this context to indicate an alternative.

3. **"like a necessary evil"**
Correction: **"as a necessary evil"**
Explanation: "as" is the correct preposition to use in this context.

4. **"not negative"**
Correction: **"not entirely negative"**
Explanation: Adding "entirely" clarifies the meaning and prevents a double negative.

5. **"but easier to deal with"**
Correction: **"but are easier to deal with"**
Explanation: Adding "are" is needed for grammatical correctness.

6. **"work to a tight deadline"**
Correction: **"working to a tight deadline"**
Explanation: "working" is the correct form to match the gerund structure.

7. **"as a medicine problem"**
Correction: **"as a mental health problem"**
Explanation: "mental health" is the appropriate term in this context.

8. **"a form of socially failure"**
Correction: **"a form of social failure"**
Explanation: "social" is the correct adjective form.

9. **"are identifying"**
Correction: **"are identified"**
Explanation: The passive voice is needed here.

10. **"unnecessary sufferings"**
Correction: **"unnecessary suffering"**
Explanation: "Suffering" is typically an uncountable noun in this context.

Here’s the corrected passage with the mistakes addressed:

Stress is often called a **21st-century** illness but it has always been with us **or perhaps** with different names. These days we regard stress **as** a necessary evil of modern living. Yet stress is **not entirely negative** and without it we will not enjoy some of the highpoints in life such as the anticipation after a date or the tension leading up to an important match. All these situations produce stress but if you can control it and not the other way around, you will feel stimulated, not worn out. However, unlike these situations, which are generally positive **but are** easier to deal with, sitting in a train that is running late, being stuck in a traffic jam or **working** to a tight deadline are much harder to manage and control and can be a significant cause of stress. Stress is now recognised as a **mental health** problem and as a significant factor in causing coronary heart disease, high blood pressure and a high cholesterol count. Patients are often willing to admit to stress problems because they feel they are a form of **social failure** and it is important that symptoms **are identified** in order to avoid unnecessary **suffering**. So what should we be looking out for as danger signals? Common signs of stress are increased tiredness, irritability and an ability to cope with certain situations.