Permissions and Security Groups
You can only change your own Security Group to one with less privileges. That is, you can't elevate your own privileges in the system. If you change your own Security Group via the "Edit Person" or "Bulk edit People" pages to one with lower privileges, you will not be able to change it back yourself. To go back to your original Security Group again you will need to speak with another person within your organization that has the necessary privileges to elevate your Security Group.
If you are currently the only administrator you will not be able to lower your own Security Group as there must be at least one Administrator in the system.