People with claustrophobia consistently report no problems with floating. However, for some, getting in the tank that first time can be a little nerve wracking.
It's good to remember you're always in control of your environment and you can get out at any time.
Before you enter the tank, open and close the door a few times to get a feel for the light weight of the door. It also serves as a reminder that there is no lock and you can open or close it at your discretion.
If you find the thought of closing the tank door daunting, here are some modifications you can make:
1. Keep the door open. While you won't gain the benefits of the sensory deprivation, there is still much to gain from having over 80% of gravity off your body and soaking in a magnesium rich solution.
2. Roll up your towel and keep the door slightly propped open. Sometimes this is enough for people to feel comfortable.
When you're ready, you can simply reach up and pull the door shut and drift away into what could be the most relaxing experience you've ever had.