Ah yes, I know a little of what you are talking about here. Your mid-pack stack looks very good when you've increased your stack with a couple of timely wins. You relax. You become a little more selective without really realizing it. Then, bang, you suddenly realize you're in trouble and you need to get more chips but the cards aren't there. Been there, done that.
What I realized I was doing was ignoring the effect of the rising blinds on my stack. If the blinds are going up, say, every 5 minutes, you can find your 30BB stack is now only a 15BB stack in just 10 minutes. If the cards aren't coming you still need to find a way. I start thinking about who I can attack at my table. I decide to apply pressure with aggressive betting but just how depends on my perception of my target and, post flop, the flavor of the board. Some times a large pre flop raise will win the blinds. Or the same bet may get a call but then I will consider a very large post flop bet. I thinking here that up till now my tight play may buy some pots. I will also consider floating to the turn r river and then shoving. Basically it's make or break time and you need to take action.