Keeping Calm

I must confess that for the last week I have been quietly fighting a sense of panic that threatens to turn into a full blown panic attack. What is causing this? Sadly I have no idea. I have been doing a lot of internalisation, trying to figure out the root of it, but without luck. It seems like the smallest incidences set off these feelings of anxiety, the likes of which I usually only experience before an important social event. Writing down my musing on the subject should help me to externalise possible causes and therefore examine them in more detail.
The most likely source of anxiety that I can think of is that in about a weeks time I will be going on holiday with my parents and youngest brother. I usually feel a little anxious before the annual holiday (or indeed travel of any kind) but never normally this bad or for this long. It probably doesn't help that my other younger brother (K) isn't coming for the first (and most important due to social duties) week. Whilst I love all of my brothers, K is probably the one that I am closest to. He knows me better than anyone else in the family and I share more of my problems with him than I do my parents. He also keeps me calm for reasons that I do not fully understand though I suspect that it is due to a shared humour, his knowledge about me, and the fact that he is a extrovert and so helps me through social situations. He won't be there for only one week, so that shouldn't be the source of all off this nervous energy.
The first time I noticed that I was more tightly strung than usual was when somebody who I don't know well enough asked me for some contact details. That always causes me to have a mini panic attack, but that was about a week ago and it shouldn't last this long. Besides, in this particular incidence I wasn't too bothered about possibly giving them due to their limited nature (they don't breach too many 'compartments' in my compartmentalised world).
It could be the lack of sunlight and the generally gloomy weather that we have been having in the UK that is negatively affecting my mood and hormone production. Sunlight has been proven to have a large impact on human health and during the winter months people can suffer from the ironically named SAD, or Seasonal Affective Disorder. It could be that, but I have been using a SAD light on the grimmest days.
Another possibility is diet, but I have been eating very healthily with most food groups covered in my diet and  missing no major vitamins or minerals. I have also started taking vitamin B complex in an effort to boost my energy levels and mood; though the science is sketchy at best about the extent to which this can help.
The future seems no more terrifying than it usually is. I am fairly secure in my job as work seems to be picking up again after a long quiet spell. I am being given an increasing amount of responsibility, but that causes a good kind of stress at being challenged. There has been no change in my (lack of) any kind of marital/relationship status, which would be the stress equivalent of a supernova, so everything is peaceful on that front.  
I have been sleeping better than usual for this time of year due to the cooler temperatures at night and the fact that I bought a fan to keep me cool, so it cannot be due to a lack of sleep. It could be partly due to me being a little exhausted by work, which is why I am kind of looking forward to the holiday.
It could quite easily be a combination of all of these factors that is making me so highly strung. I haven't really had time to metaphorically 'sit down and take stock'. I guess that I should try to get back to the basics of my life and focus on the things that bring me an almost primeval sense of comfort, for example bushcraft or one of my SI's. Rule number 32: Enjoy the little things.