Panic Attacks can sneak up on you when you least expect it!
For example, I remember my first Panic Attack VERY well. I was in High School and my parents were going through a really rough patch in their divorce, and I had to carry a lot of the burden in helping my mother out. That day I woke up like any other, walked into school, and went to my first few classes - when all of a sudden, I felt my heart start to race, I got sweaty and felt like I was going to pass out. I asked to go to the nurse and when I got there I felt like I was going to faint, I started to legit get anxiety because I was scared and felt sick to my stomach. I broke down into tears I was so freaked out.
The nurse listened to my problems and checked me out to see if anything was wrong before she gently knelt down and told me I was having a panic attack and to breath into a brown bag she had, after doing so for a while she called my mother to take me home.
So the anxiety had been building up inside me for... probably WEEKS at that point before it finally erupted into a full-blown attack, because my panic attack was caused by something other than HA I feel like I didn't pay much mind to it, but when your attacks are the result of HA it's worse because you worry when you are having panic attacks, and when you aren't and feel 'fine' (with the symptoms still) you get nervous and wonder if it really IS something serious. It's a vicious cycle.