Assuming age of your father around 65-70 yrs seeing yours 40 yrs, it may be a simple cold to something serious like lung infection or more.
Plz elaborate more like exact age, smoking alcohol drinking habits, any pre existing diseases like
Diabetes, hypertension, Tuberculosis, COPD or asthma. Any medication he is taking now.
Next Steps
If pt is critical or grossly unstable immediately see a specialist doctor at earliest
Health Tips
Don’t wait to consult
Stop smoking and drinking with if doing before
Not to strain or stress