Long term effects
Bipolar disorder tends to be lifelong, rather than a short-term problem, however there are often long periods of "normality" between phases. It is serious though, and if left unchecked and unmedicated it can be disabling.
Numerous studies show that bipolar disorder affects a person's ability to think and perform mental tasks, even when there are no active signs of either depression or mania. Other people with bipolar have shown that, with help, it is still possible to lead a relatively normal life.
Short term effects
The two phases - mania or depression - "cycle" or change, and this varies greatly from person to person. Some people spend a few days in mania before coming down (or in depression before coming back up) whereas others may spend weeks or months in one phase.
People may switch straight from mania to depression or vice versa, or have a period of "between" in which they behave normally.
Between cycles, people may feel that this time it has all stopped and they can discontinue their medication; it is important to continue the medication until the treating psychiatrist says they can wean themselves off the drugs.