I've noticed this tendency too. Being aware of it is a huge plus and you're already well ahead of many players by being mindful of this tendency. Notice it and tell yourself/remind yourself to stick to your game. And this applies whether you tend to get a little looser or too tight when you're up with a big stack.
Also have to consider stack sizes so can't be afraid to make calls that make sense just because our stack is bigger. But definitely be mindful of changes to your play when your stack is big.
As others said you could also decide when you're up a few buy ins at a table to leave if you lose X amount of the profit. I was playing online other night and was doing well and made a call on a river that knocked at least a buy in worth of profit off my stack. While it wasn't the worst call and I had reason to suspect the villain was over valuing a weaker hand/
bluffing on a missed draw; it impacted my game and so I left a few minutes later to protect remaining profits.
You might also consider the Ferguson method concept of leaving whenever your stack on table represents more than 10% of your
bankroll. But sometimes as long as you're comfortable playing super deep, you're leaving value on the table by leaving when up. I prefer to play until i get tired or notice myself loosing focus or making mistakes and if i do lose a chunk of profit I consider taking a break or leaving with the remaining profit.
Bottom line: Once you start questioning whether you should make a call because you're afraid of losing the profit (and the call is sound and makes sense), it's time to consider getting up from that table. And if you feel you get too loose when up, then again focus on whether or not the call/play makes sense. Don't open your range to gamble with the profits.