Federal regulations require Title IV financial aid funds to be awarded under the assumption that a student will attend the institution for the entire period in which federal assistance was awarded. When a student withdraws from all courses for any reason, including medical withdrawals, he/she may no longer be eligible for the full amount of Title IV funds that he/she was originally scheduled to receive.
The return of funds is based upon the premise that students earn their financial aid in proportion to the amount of time in which they are enrolled. A pro-rated schedule is used to determine the amount of federal student aid funds he/she will have earned at the time of the withdrawal.
If you drop a class and maintain the same level of enrollment and credits, your financial aid award should not change. If you make this change before the end of add/drop and can "add" a course with the same amount of credits, your award should not change.
If your overall enrollment status changes, your aid may be adjusted, resulting in owing back funds.