Revealing mistake: At the start after the main title appears you can see the outside of Haddonfield University and you can easily tell that the building is a digital composition. (00:16:10)
Revealing mistake: When Dr Mixter is talking about Carl Jung in the classroom the camera pans over the students and if you look at the blonde girl with the pink sweater on she stares at the camera for about a second. (00:16:35)
Revealing mistake: When Deckard and his friend are in his bedroom on the computer you see a window beside him and outside you can see that there are painted clouds on a wall. (00:20:20)
Revealing mistake: Freddy's car is parked outside Michael Myers' house twice. First, when the trunk is open with the adapted machine and then he parks on the other side of the road after Charlie gets killed. (00:27:15 - 00:30:00)
Revealing mistake: When you see Freddy's car parked outside the Myers' house when the trunk is open,you can easily tell that the background is artificially created and there is a wall at the side with painted clouds. (00:27:20)
Revealing mistake: After the hallway camera cuts out, it eventually comes back on the computer screen that Deckard is looking at. If you look at the landing and the stairway, the picture is reversed. (00:40:05)
Revealing mistake: When Michael is hung from the window, an upwards shot reveals the top of the sound stage the Myers house was built in (top right corner). (01:13:42)
Revealing mistake: At the end of the film the garage is on fire and just before Freddy bursts through the door, there is a really quick close up shot of Deckard kicking down the door. (01:16:30)
Revealing mistake: When Jen is decapitated, its blatantly obvious its a fake body.
Revealing mistake: When Jen has her head cut off, the cord to the camera would be severed too, yet it is still broadcasting when her decapitated head is lying at the bottom of the stairs.
Revealing mistake: In the H20 flashback when Laurie cuts the head there is no blood from it.
Answer: At first impression, Laurie was catatonic not only from the shock of killing an innocent man, but also from a lifetime of being chased down by her murderous brother. She obviously knows from past experiences that nothing she does (including faking her own death) will stop Michael from finding her. It is later revealed she has been faking her mental issues (think when she has been hiding her regular meds in the raggedy Ann doll) and is committed only to stopping Michael, no matter what the cost. She may have also been trying to protect her son and the only way to do that is to allow herself to be institutionalized in order to lure Michael there.