There may be various causes for this feeling. You should STOP, BREATHE, THINK, and ACT.
- Signal, if you are able, that something is wrong to your buddy, and SLOWLY begin ascent procedures.
- Check the depth and pressure supply (submersible pressure gauge, or SPG) while ascending.
- Ensure that you concentrate on buoyancy control during ascent.
- When reaching the surface, concentrate on establishing positive buoyancy.
- Signal to the surface support for assistance.