During the Bull run period, my decision to sell my Altcoin will depend largely on my expected market price. if currently, the price of my Alt coin "A" is 0.01.
And my expected market price for my Alt coin "A" is 0.5$. I might usually be reluctant to sell my that Alt coin during the Bull run if it happens that the coin rises to 0.05$.  
Although there is obvious spike in market price of that coin, spike in market price is not up to my expectation. hence my reasons for being reluctant to sell.

My point is, bull run may come alright. but if traders expectations are not meet most traders will obviously be reluctant at selling their coins and will decide to hold.
Bull run does not always mean profit. In my opinion, it basically mean you have held me for so long, sell me out and regret later. Or don't sell me at all and regret for not selling me.  it puts you in the position of being restlessly indecisive if you have not prepared for it. And account for what is basically term panic sales.
Be smart.