Get Over It
There are many answers to your previous question that point this out, but "ooo someone might die" is well within bounds of normal lethality of a campaign. Many GMs will warn players "Very likely, one of you is going to snuff it" when going into a majorly tough leg of the campaign. Frankly in this case if I were your GM I would have killed a character already to get you over whatever bizarre hangup you're having about it.
Question 1: "We had some close scrapes and someone could have died!"
Question 2: "Things are getting worse and really now someone is likely to die!"
I am eagerly anticipating question 3, "A character died in my party, how can life go on?" (Not really.)
Characters die. They're fictional characters. You are setting yourself up for a lot of unhappiness by tying so much of your emotional state. In fact, in good stories often someone dies and that's part of it. If your group isn't willing to risk their lives in situations like this they shouldn't be adventurers, they should be part of the huddling masses of commoners waiting to be saved.
One PC dying every single session is an unusually high rate - see A PC dies every session - bad tactics or the normal outcome of adventuring? - but in a usual D&D game, occasional death happens and is usually considered a normal part of the game.
Your PC needs to have a personal crisis moment where he finally stops whining about "oh this is hard we may die" and pushes through it to "OK guys, lets go kill this freak." Here's how you do that.
It's reasonable that you can't rest and your GM is not "forbidding" it, he's telling you that your character, a denizen of that world, can see and understand there's patrols all over the dungeon and if you do hole up and try to rest that rest will be disrupted in 20 minutes by the dungeon security guard coming through on a door check. That's fair, resting in a dungeon is not always possible. Depending on how much time you have in your race vs the clock you could withdraw, short rest, and go back in - the foes may reposition into the cleared parts of the dungeon but there shouldn't be more of them (unless they are summoning/raising dead/etc). But other than that:
- Avoid pointless fights - in a dungeon, the thing that depletes your resources is fights. You are not there to "clear every room" you're here to stop the Eye of Gulga Grimnar. Note that doesn't even necessarily mean you have to kill the boss. Start thinking smart. What has to happen to end the threat, and what's the lowest effort way of doing that? How is the laser controlled, is there a control widget to steal? Can it be broken? Can you bypass guards and go straight to the boss? Maybe you need to actually take a prisoner and interrogate them, they tend to have "information."
- Get healing/magic/etc - In a dungeon, the thing that restores your resources is someone else's stuff. You can target killing or parleying with people to that end. You seem low on clerics. Take an opposing cleric prisoner and make him heal you. Try parleying with isolated people - often in adventures like this there are "factions" where maybe someone is looking to overthrow their boss and they may be evil but aren't into the "laser death plan." "Hey let's go kill your boss, you get to be in charge but we break the laser. Deal?" Then you have more fight on your side = less PC resources expended.
There's a million ways to play smarter, but those are two of the pillars thereof.
This is basically the same answer as to your previous semi-identical question, How can I suggest the DM stop trying to kill us?, but more direct and tailored to your current situation.