I have started at 2NL and now play 10NL, hopefully by end of year I will be ready to try 25NL.
As for your question, you need to say what kind of strategy you play (stack size, how many tables, style of play).
Generally speaking, I play when I am in the mood and don't have a set number of hands. I do like to take breaks between sessions to rest a bit.
If I have a big stack on a table and I think it is risky to continue until the inevitable bad beat then I quit the table and open a new one. It just makes it simpler to play since 100bb stack is easy compared to 250bb stack, which gives everybody great odds
for set mining and such.
Your problem (if it is one) might be lack of concentration/discipline when you are up and then you spew, or the mentioned stack size issue. It is common to have several players on a table with 130bb+ stacks and if you have them covered it becomes very tricky when raising from EP/MP.