Can anybody tell me if this episode of CHF in Jan2015, is a one-off situation or there is history wherein there is a change of more than 5% in any currency on a single day??
Since a lot of traders witnessed that event that day…the conclusion stays the same - Anything can happen in the market at any time.
My question is , "was there another occasion like this " in the Forex market history ?
I dont know about forex history, but there are plenty of instances of currencies massively losing value, albeit over weeks or months not minutes. For example the German currency fell from 90 marks to the dollar in early 1921 to over 300 a few months later, then to 800 during 1922
The main reason future moves could be quicker is online trading and computer run sell programs dumping currencies as soon as a selling trigger is hit
Anyway… nothing extra ordinary should be a shocker to anyone after what happened to the CHF january 15.th this year…it came without any warning. Expect anything to happen at any time and secure your positions and your capital for as best as you can.
As Eddie mentioned - automated trading and HFT can if the market gets a little offset or hits massive amounts of orders at a spesific price trigger massive moves in just seconds or less… how massive nobody knows. I was trading yesterday on the eur/usd…and in less than a tenth of a second it made a 30 PIP gap on my 1 and 5 minutes chart… when computers trade against eachother…it happens fast 
And that is just ordinary trading…
It’s true you don’t see moves that big in such a narrow time frame in the major currencies very often, but as others have suggested, you should always expect volatility events. If you get away from the majors, and especially into the more regional currencies, you will see a much higher frequency.