Stamina, Energy and Health will normally replenish at the rate of 3 minutes each. If you have an Arms Cartel Gold Card they will regain at the rate of 2 minutes each. Although the difference seems minimal over the course of a day if works out at 720 Stamina, Energy and Health instead of 480.
Having negative health is the result of being hitlisted multiple times. To restore your health either visit the hospital or wait for it to regain over time as long as you are not attacked again (after your health regains past 26) or you are hitlisted again.