Nuu - congratulations on the 3 months. I enjoy watching you transform in your journey. I am sorry about your panic attack. Do you meditate? Dee's suggestion of belly breathing is often how I focus on my breath in meditation. Its a technique I learned in yoga. When I competed in triathlons I found this breathing technique could be used to slow my heart rate to keep it in the zone I needed it in (used a HR monitor to do this). I find may of us take very shallow breaths and can hyperventilate. This is often seen in a new swimmer in the pool. Interestingly, as babies and children we breath naturally through the belly and then over time somehow transition to shallower chest breaths. Like most good things, I find going back to the traits of children can be useful.
If you feel faint, cold towel and lying down can help too. Perhaps this is your HP sending a message...maybe to slow a little and be gentle? Maybe its just a panic attack. Either way I wish you the best!