To slow down... or not to slow down?

Do both.

If you're too stressed by the tempo, you'll make mistakes. If you never push the tempo, it's difficult to get faster. So spend most of your time playing at a comfortable pace, so you can concentrate on your technique. Spend part of your time pushing the speed. If you make a mistake, drop back to a comfortable pace, make sure you can still play it perfectly, and then try pushing the tempo again.

In general, if I make a mistake in practicing something, I IMMEDIATELY slow down to where I can play it right. If you don't do that, you risk practicing your mistakes and making them habit. But stepping outside our comfort zone is how we make breakthroughs in our ability, so try it fairly often (at least once every other day at a minimum would be my advice)

Thanks! If I spent some time playing accurately, how much should I increase the speed? If I play comfortably at, say, 80 bpm, then go to 85 bpm, what if I still play fine? Should I increase the speed even more? One day I can play comfortably at 85 bpm, then 80 bpm again.

80 bpm to 85 bpm is a fairly large step. I suggest a stopping point at 83.

You need to get acclimatised to a higher tempo. If you go from 80 to 85 in one day, you need to spend a couple of days at 85 so the fingers and the head get used to what's happening and when. Then you can up the tempo to 88.

I find the 3 bpm increase followed by a 2 bpm increase works well - 82 bpm is too much like 80 bpm and the bigger step to 85 bpm feels like a bigger step.

i used to just play a little fast. that was all i'd try to do. not on a metronome, just audibly or physically noticeably faster than my normal speed. i'd get somewhat comfortable playing at a speed, then play a little faster, maybe right away, maybe a few days or weeks later. i just left that up to my hands to decide. i didn't really push it too hard, or play as fast as i could much. i didn't practice shredder scales or anything, i just improvised at a pace i could keep up. not so fast i'd miss notes or anything like that, and not slow, but fast enough that it was sometimes a little rush to fit the end of a line in before the end of a bar or something. that's how i approached improvised lines. for rhythm playing, i just play the snot out of the thing sometimes, almost like a drum. you don't have to try to play superfast all the time. just play kind of fast, but in control, and not like that all the time, either. the speed will just continue to slowly creep up until you start to slow down intentionally or age catches up to you. it took me about a summer before i got bored with trying to play fast. i was as fast as the shredders, but it was unnecessary a lot of the time.
remember, if you push it too hard, you'll get frustrated or get carpal tunnel. i didn't play much with a metronome, either. i just check against it every once in a while to make sure my timing isn't off. i find them annoying, but if they don't bother you, go ahead. playing and listening creates deep rivers of nerve ending in our brains and fingers, and you can't really rush that, but you can listen to a lot, and play a lot, and that helps. try to keep your hands loose and avoid brain trauma. i.e. don't drink too much. it killed bonzo and broke up or ruined more bands than you can count.

Once I get out of the comfort speed, I worry and so can't play.

Yeah but, If you practice something slow and get it right, you gain confidence in the thing you're playing and the worry goes away. Then you speed up til you screw up, then slow it down again. I use a slow down program for everything I'm working on.

Thanks everyone! Seems like I should make speed increases smaller, but push myself more often. Will try.

i'm just telling you what i did. that doesn't always mean it'll be the same for you.