After his team made changes since the last race in Jeddah, the seven-time world champion said that the car felt the best it had ever felt at the start of FP1.
However, following set-up adjustments he reported that it got "worse and worse," and that ultimately in FP2 he felt the "least confident" he has ever been with the car.
He finished the session in 18th place.
"I obviously don't feel great," he said. "We had one of the worst sessions I've probably had for a long time.
"FP1 generally felt quite good, the car in FP1 run one felt the best it's ever felt.
"And it just got worse and worse. And then we made some big changes into FP2, and it was tough."
He added: "After that session, I feel the least confident I've ever felt with this car. But there are positives from that FP1 run that we did."
Hamilton's team-mate George Russell had a better day, taking third spot in FP1 and sixth in FP2.
"I felt pretty comfortable out there from the beginning," he said. "We made some changes since Saudi and Bahrain, we're still trying to understand this car further.
"Every single lap is so valuable, you're learning more and more about it, and trying to get it into the sweet spot.
"Obviously, now we have a team back at the factory working on the sim, we're trying to get more performance out of it.
"So let's see what tomorrow brings. Always when everybody has a good night's sleep the next day it's often very different."
Nevertheless, Russell admitted that it had been a scrappy day at times.
"We're pushing the limits, and a few little moments here and there," he said. "But all under control in the end. And it seems pretty tight out there. In the first session, I think it was like two-tenths splitting 10 cars.
"FP2, slightly more spread out. I was on course for a really good lap at the end, and just had a small problem in the last two corners.
"On my very last lap I was I think two or three tenths up. I came out of Turn 12 and I damaged my front wing.
"And I went off the off the track in the last few corners. I didn't go off, but I lost loads of lap time there. So I think we would have been P3 in that session. But we've always had quite strong FP1 and FP2 showings."
