When do you tell someone to "Get a grip!"? When they are freaking out, spinning and panicking. Get a grip means to focus on what is important to your goal and shut out the other distractions.
Do you...
1) know clearly what the goal is?
2) know what is critical to reach it?
3) know how to manage everything ELSE while you do what you must?
4) know what tools you need to help you?
5) know what the next clear step is?
Answering these 5 questions means you have a good GRIP on your situation.
Assume your boss tells you there is a major problem with the firm's biggest client and she wants you to "get a grip" on the situation. You would know that you need to review what's happened, distill the situation into it's essence and figure out the next, clear step.