Being sick while pregnant certainly isn't fun. Having the flu while pregnant is even worse. But being down with the flu during pregnancy might be linked to longer term concerns, too.
Using alcohol to cope with symptoms of a mental health issue can result in alcohol dependence. Short-term alcohol dependence can easily turn into long-term dependence.
Some medications are linked to disorders such as autism or to birth defects when taken during pregnancy. However, that risk must also be balanced against the medication's benefits.
Not every mental health disorder fits easily into a category. Some slide on a scale between two well-defined disorders.
Bipolar disorder is not a mental disease you can "catch." But there are childhood experiences that could be related to how severe the condition is for those who have it.