WRITTEN BY BUTTERNUT / SHRIMP SYSTEM
To put it simply, a headspace/innerworld is an internal world where alters can be themselves and experience things you couldn't experience in the outerworld. A headspace is a tool used in therapy by both systems and singlets. Some systems do not have a headspace, others have had a headspace for as long as they remember, and some want to make a headspace. All are valid!
No, they cannot. Alters can split, fuse or go dormant and in the innerworld, and it may even appear as death, injury, pregnancy, etc, but it isn't actually. When things that make no logical sense like this occur in the innerworld, it is likely metaphorical for trauma and/or stress.
Some systems have accounts of being sexually assaulted in headspace. Often, this is a metaphorical manifestation of previous traumas. If an alter sexually assaults someone in headspace, it likely feels real and painful because you have experienced it before. Other "physical" injuries taking place in headspace can also feel real and/or painful because of similar or even the same reasons as sexual assault. Anything like this can potentially leave you with phantom pain when fronting/being in the body because your body remembers the feeling of these types of events.
In systems with a headspace, some alters may find themselves unable to access some or all of their headspace while other alters can access most or all of it. This is not an uncommon occurrence, and there are many reasons this could happen. It may be to protect some alters, it may be due to denial, due to lack of communication, due to unawareness of the headspace or system's existence, etc. It is normal to not hear or see anything from any part of headspace. It is normal to be able to see headspace in vivid detail. All experiences are valid.