what do you mean by the fact that the low of the candle......
Simple, the low tick of the candle with the largest volume had been taken out - price had gone below it - all long positions from that high volume candle forward were losing money causing sell stops to be activated.
now, i read somewhere on the book a P-shape usually shows during an uptrend. I guess that does not include any sign to tell when a trend cease to exist. How could I tell if that's the case?
A "P" shaped profile simply shows that the market has found value at the upper portion of its range. That value area can be rejected in either direction as price searches for more liquidity.
I read in another post of yours that you have some programming skills. Isolate all "P" shaped days and check what percentage of the following days are up days. You may find a statistical edge. Keep in mind that all "P" shaped days are not the same - some close above the POC, some below, some close above value, some close below, some close in the top or bottom 5 percentile.
I probably should have traded using a 1-min chart. It looks much worse in a 1-min chart than the 5-min one.
does that large black candle with a significant volume right before my entry voids the whole trend?
Trend is relative to the time frame you are trading - a 1 minute trend and a 5 minute trend are two different things. As a rule you are going to want to be using a larger time for trend and a shorter time frame for an entrance signal.