Can anxiety attack happen out of no where? i was taking a shower and my heart just started beating really fast and i was shaking

Yes: At least it is quite possible that you did not notice a reason - that's a bit different. Busy, distracted people can miss signs of trouble and it may be a function of anxiety symptoms to get your attention. One of the skills you can learn in CBT therapy is how to be more aware w/out your body needing to scream at you. It can really help you know more of what's happening with you. Best!