Is ischemia serious? Needs to be taken?

My wife having difficulty in breathing at Sunday night. We see a doctor on Tuesday. ECG done and shows a change and doctor says its called ischemia but nothing serious and not to worry. Immediately we have done echo also which was completely normal. Doctor says everything is ok and nothing to worry but prescribed ecosprin tabs. I have confusion here and keen to know 1.how serious is this or can I ignore this as said by Doctor that it is normal. 2.Will it bring some serious issue later. 3.It is just came and go type issue or its a lifetime disease that need to carry 4. What might be the cause having this at the age of 35? 5. her family and any relatives doesn't have any cardiac history ever 6. What are the precautions needs to be taken?