Really what you're describing is simple fear of change. You've spent your whole life studying and now you see the end where the bulk of your time is not studying any more. You can go on to make a career out of studying but again that is an extremely competitive field and if you didn't plan for that before now it can be difficult to get in to.
It sounds like you've fallen for the marketing trick to keep people unhappy. The idea that you have passionate about something in order to do it and to do it well. That kind of marketing is great to keep you unhappy and continuing to throw money in various directions to pretend that a passion project is what you need in your life. It's a lie. What you need is probably something you've never been taught, you need grit. Grit is what keeps your grades high even when you're unsure about what's next. Grit will make you the best intern that a company has ever seen. Grit means that you don't have to like the task in front of you but you'll damn will do the better than anyone else. Grit is the difference between someone who achieves while others whine it can't be done.
When you've developed grit you've found true passion. Passion for thing means that thing controls you and if that thing changes (which it always does) you're plunged in to depression. When you can redirect that so your passion is about personal achievement regardless of the task you've found the grit to continue and passion you want.