You can sleep with them beside your head if the field doesn’t interfere with your nervous system. Anywhere close to your body will work.
I’ve slept with the dog tags close to my body with the chain removed, or worn on my arm as @SC448 suggested, and both have worked well for me.
They’re effective anywhere within your aura, so typically about 1-2 metres from your body.
They may be more effective when touching your body. I’ve found that to be the case. They may also be more effective closer to your body than further away.
Perhaps the effective distance would be less for you if you’re very ill, because long term illness has a tendency to weaken one’s aura, so you may want to keep them a bit closer to you.
You might also wish to use the Energy Expansion card from the Dreamweaver card system to strengthen your aura/energy body, and the Healing and Chakra Stimulation cards to aid in healing.
It’s perfectly fine to wear Advanced Healing and A.P.E. as much as possible, especially as those are fields meant to help with healing and regeneration.
Some fields like Unlimited Energy or Productivity Enhanced might be best not worn to sleep as they can interfere with rest, but most fields can be worn all of the time.
I’ve found that at times I assimilate the energy of the items more while sleeping, and I wake up more refreshed when I sleep wearing the A.P.E. tag.