The Mexican provided a bizarre end to first practice when he locked up and slid into the barriers at the pitlane entry, while he spun across the gravel trap and nudged the Turn 8 barriers in the second session.
Perez said both mistakes had been caused in part by the unpredictability of McLaren's 2013 challenger.
"It was a very difficult day for myself with the crash in FP1 and the off in FP2," Perez said.
"We don't really understand what happened: I had a lot of wear, the front tyres were losing temperature and as soon as I hit the brakes I locked the tyres, [but I was] not pushing at that point.
"I'm not very confident with the car and that makes things difficult.
"We have so many question marks, we have to analyse everything that we have done because we don't know which direction we are going. The car is so inconsistent for us."
Perez did insist however that there had been positives from the first day, particularly given the amount of data he and team-mate Jenson Button were able to accumulate.
"There's no magic; we're still learning, and today was very important," he said.
"I will start from zero tomorrow, with a completely new set-up. This [doesn't] make things easy but I think we are able to learn and go in right direction for future.
"I'm confident we can make Q3."