I think I can get "your back" on this issue

. First things first though. Ditch the B vitamin idea ASAP. B vitamins, primarily B complex are very stimulating to the nervous system, while B's have their benefits a calming effect is not one of them and that is what you need...CALM...
As for
Lexapro, personaly I would try another med first. Lexapro is quite potent and highly selective which is why so many people have difficulty trying to stop taking it. Lexapro can just as easily make you feel worse as it can better. SSRI medications can be very tricky, they ALL have side effects, EVERY one of them. However, lexapro (in my oppinion and experience) is one of the worst. That is not to say that many folks are not happy with it but, most of those people have not tried quitting it either.
At the age of 27 and not having a history of anxiety or panic (unless you did not mention a history) my conclusion of the problem would not be a diagnosis of a disorder but rather, an over abundance of stress. This does not have to be recent stress either. It can be the accumulation of years of pent up stress. The panic and anxiety are your body's way of saying "hey, you need to chill." In the meen time, you are left feeling totaly zombified and "out of it" racing heart, can't breathe, breaking out in cold/hot sweats, jittery,etc...So, now to cope with it all.
Yes, medication can help but, medication will not CURE the problem. There is nothing wrong with taking medication to help you get through this rough time but, please try to keep medication treatment short term as you educate yourself on other effective ways to treat and cope with the problem. Also, keep in mind always that this is likely only a temperary problem and try not to worry that this will last forever.
It is VERY RARE for anyone to develope Panic disorder past the age of 23 and even less likely for men.
You did say that you work out correct? Is there any chance that you have been overdoing it? I ask because the panic and anxiety symptoms can be a result of magneseum depletion....It is quite common for people to develope vitamin and/or mineral defficiencies from excessive excersize as well as for folks who are simply very active. I know that you said you had blood work done however, it is highly unlikely that your doc would have checked your vitamin/mineral levels...it's just not standard proceedure unless you are anemic or have serious health prob's. Also, do you take any calcium supplements? To much calcium will deplete
magnesium...Magnesium calm's, calcium activates. Would you provide a list of all vitamins and supplements that you may be taking now? I can tell you what to cut out and what to keep etc, for the panic/anxiety.
As for the medication. If this were me, I would try
celexa instead of lexapro. Celexa (citalopram is the generic) is the parent drug of lexapro but, it is far more mild. Another to consider is
Paxil (paroxetine is the generic). Stay away from
prozac,
zoloft,
wellbutrin and SNRI's as they are not well suited to anxiety/panic, they are simply to stimulating and tend to induce panic...(I have been on them all at one time or another)
You could take an anti-anxiety (benzodiazepine) for the panic attacks.
Xanax is best suited for quick relief of panic attacks because it is the fastest acting benzo however, that said; I must caution you on benzodiazepines: It is O.K. to use them as needed SHORT TERM....long term use of benzo's can lead to dependance and/or addiction. The typical starting dose of xanax for panic is .5 however, if you get a script for xanax please ask your doc for the LOWEST DOSE which is .25 (I think everyone should start at the lowest dose of anything and go up as needed)
On a personal note: I reccomend to ANYONE who is contemplating the use of any medication especially those that are neurologicly active (ie: Brain drugs) to first try older med's as oppossed to the newest supposed latest greatest med's on the market. The reason for this is that the older med's have been in use longer and therfore have been studied for long term effect etc, The newer the med, the less that is TRUELY known about it. I hope I have not scared you as, that is not my intent. I only wish to educate and help you as one who has experienced all this.
Regardless of what choices you make here are my reccomendations on supp's: fish oils 3 x's daily, Magnesium as directed, Good quality multi-vitamin.
You can try Noni juice for depersonalization(you know that feeling of unreality, like you are there but not there) You can buy it at wal-mart; it has worked for me besides it tastes awesome

Also, as an alternative to benzodiazepines you can take Passion Flower capsules it works on Gabba very similar to a benzo without the undesired potential side effects....More on that later if you are interested....I know that I have left out ALLOt but, if you have questions PLEASE, fire away...I hope this has been helpful...Peace....Erin
P.S. I am NOT a doctor, just a person with experience. Double check ALL advice with your doctor and/or a nutritionist!