I'm not a futures trader, but something similar happened to me. I started by trading equities and after a relatively short period of time, my account grew ten-fold after I sold some property. I tried to think in terms of percentages, but this didn't work well. How could it? I'd spent months treading a $20 loss as large and a $200 loss as devastating, and now I was trying to treat $1,500 as minor! It just wasn't going to work.
Not that I didn't try. I traded this way for a month and just bled money. I was consumed by greed and fear. The stress of the money gave me tunnel-vision. I couldn't see things properly anymore and was making one mistake after another because of it.
After a month, I stepped back and reduced my size to a minor fraction of my account. It was still larger than when I started trading, but it was small enough that I wasn't going to care much whether I won or lost, letting me focus on the trading.
With time, I grew comfortable with the level of risk. Perhaps it was just familiarity with the numbers on my P&L column, perhaps it was consistency and profitability, I'm not sure. After I felt that I'd proved myself able to trade at one level profitably and consistently (surely this means different things to different people), I would increase my risk and observe how I traded.
After five months risking between 1/16th and 1/4th of what I was when I first got the money, I've more than recovered my losses. I just doubled my risk last week and my friends have been saying I'm "ballsy" and "gutsy" to risk so much. I don't see it. I don't feel scared anymore, I don't feel like I'm gambling, I don't feel like I'm doing anything gutsy. I know intellectually that the money is substantial, but because I've come here slowly after proving it to myself, I can look at it relatively dispassionately.
I will say that after each increase, there is a period where I must mentally and emotionally adjust to the new level of risk. For that period I trade very conservatively and rack up some quick and easy profits. After this, I relax a bit more and become more aggressive, shooting for more speculative trades which have proved profitable in the past but which entail a greater emotional roller coaster
Hope that helps. I wish I could offer more insight, but I'm learning also.