Anyone else forget to eat and drink?

From an autism perspective, all of the issues that you've described are associated with interoception; this is our internal sensory system, which is one of our less-well-known senses.

Just as autism can cause us to be under-sensitive (or over-sensitive) to other sensory inputs (eg having a very poor sense of smell, or preferring very spicy foods due to an under-sensitive sense of taste), so we can also have unusually low (or high) levels of accuracy with our interoception, causing us to not notice our internal body signals - including our hunger, thirst and toileting needs.

I have similar issues to you at the moment, but I find that my (autistic) reliance on routines is a big help. Perhaps you could try to develop some yourself. Annoyingly, our autism can also make it difficult to do this, but - for me - persistence with developing new routines works eventually, although it can take some time. 

I also use a smart water bottle and app.

Developing consistent routines is actually one of the strategies suggested by Reframing Autism for supporting ourselves with these kinds of difficulties. You might find their advice helpful. It includes:

• Engaging in Interoceptive Awareness Training
• Involving Visual Supports and Communication Tools
• Providing Consistent Routines
• Modifying our Environment
• Making Space for Stimming
• Upskilling your knowledge of interoception (ie learning more about interoception, then sharing that knowledge with those who support us, including our family members)

All of these are explained in more detail here:

Reframing Autism - Interoception: Knowing Yourself Inside and Out > Strategies to Support Autistic Individuals with Interoception Difficulties

Given the extent of your struggles, and that you're not getting on well with using aids like alarms, I also suggest talking to your GP, who should be able to provide support. 

From an autism perspective, all of the issues that you've described are associated with interoception; this is our internal sensory system, which is one of our less-well-known senses.

Just as autism can cause us to be under-sensitive (or over-sensitive) to other sensory inputs (eg having a very poor sense of smell, or preferring very spicy foods due to an under-sensitive sense of taste), so we can also have unusually low (or high) levels of accuracy with our interoception, causing us to not notice our internal body signals - including our hunger, thirst and toileting needs.

I have similar issues to you at the moment, but I find that my (autistic) reliance on routines is a big help. Perhaps you could try to develop some yourself. Annoyingly, our autism can also make it difficult to do this, but - for me - persistence with developing new routines works eventually, although it can take some time. 

I also use a smart water bottle and app.

Developing consistent routines is actually one of the strategies suggested by Reframing Autism for supporting ourselves with these kinds of difficulties. You might find their advice helpful. It includes:

• Engaging in Interoceptive Awareness Training
• Involving Visual Supports and Communication Tools
• Providing Consistent Routines
• Modifying our Environment
• Making Space for Stimming
• Upskilling your knowledge of interoception (ie learning more about interoception, then sharing that knowledge with those who support us, including our family members)

All of these are explained in more detail here:

Reframing Autism - Interoception: Knowing Yourself Inside and Out > Strategies to Support Autistic Individuals with Interoception Difficulties

Given the extent of your struggles, and that you're not getting on well with using aids like alarms, I also suggest talking to your GP, who should be able to provide support.