My girlfriend suddenly just woke up with heart pain she is 27?

she said she felt a tight sensation around her heart and no other symptoms it happened very suddenely in her sleep. this is the second time its happened in the past 2 weeks. She has been very busy with work lately and the first time it happened the doctor said its exhaustion. She is korean and we live in Seoul but to be honest i dont trust the doctors here compared with the uk. Any ideas?