Taking a multivitamin is absolutely a good idea, especially if you're not eating well. However, I'd question as to why you're discounting the idea that you're having anxiety issues, especially after suffering a panic attack.
There's an old expression that says that when you hear hoofbeats, you should think of horses, not zebras. I say this because you're a college student, which is often a stressful period in life, and usually includes ingestion of alcohol or some form of drugs, all of which can alter or effect your mental state.
You'll be the only person who can really answer your question. While It's unlikely that you'll have a severe-enough vitamin deficiency to cause an altered mental state, it is vaguely possible. Anxiety is more likely, in truth, but you can rule out vitamin deficiency by consulting with a medical professional and improving your diet. As for the potential for an anxiety disorder, you can answer that right now, based on how you feel about your general life situation. If it's stressful at times, and affects your quality of life, anxiety may be an issue for you. Regardless, help and treatment are available for both!
You will not be getting all the essential vitamins, minerals and amino acids just eating junk foods. Also, nutritional deficiencies have been linked to junk food cravings. The number one symptom of vitamin B12 deficiency is fatigue which you haven't mentioned. Magnesium is a common cause of anxiety and panic attacks and is easily depleted eating junk food. Changing your diet and taking a good quality multivitamin is recommended.
Hey sorry that your going through this. Have u seen a dr. If not that should be the first thing u should so to rule out anything serious. If it is a vitamin b deficiency the dr will let u know. Anxiety has the same symptoms as u describe but I'm no dr get checked with your dr first and let us know