You are quite young to have a hear attack! - it is unusual but not unknown...
But you have been laying the foundation - smoking
And now high cholesterol
- though there is good and bad cholesterol, it is almost alwyas the bad one that is high in most people.
Pain from the heart is generally in mid-chest / brought on by effort / relieved by rest / radiates to shoulder or arm etc. Of course, there are exceptions...
The last two digits of height in CM give an approximate weight! 64 Kg! It is good that you have started to reduce. It will be better if you stop smoking. More so, if you adopt diet, exercise and may be drug for cholesterol
No need to be scared - of course you must be concerned. The very fact your GP sent you home means things are not that urgent - but need more attention.See your doctor, have a complete evaluation - you are very young and and with proper care, youcan look forward for a long and happy life
God bless you