Moodle has many different ways of calculating grades.
One common method is what Moodle calls a ‘Sum of Grades’ aggregation. This means that Moodle adds up all the points you’ve earned (186, in the example below) and divides that by all the possible points (200) to get your course percentage/grade (93%):
This is great when all of your assignments have been graded and are in the system. However, when the instructor adds an assignment to Moodle, but doesn’t enter a grade for you for it yet, that can falsely (negatively) impact your course total.
This is because your total number of points earned hasn’t been updated yet, but Moodle looks at all of the possible points (300 now, example below) including that new assignment. So, for the example, instead of dividing 186 by 200, Moodle divides 186 by 300, giving you the much lower course percentage (and, hence, the heart attack!):
To find out your more accurate percentage, take the possible points for the course and subtract the points for whichever assignment(s) has not yet been grades (300-100). Then the number of points you’ve earned for the course and divide it by the number you just calculated (186/200=93%).