Since last saturday I've been having constant anxiety attacks and its now been a week and my heart seems to be calm when I lay down but when I get up and walk and begins to beat faster. What could be the problem and what could I do to solve it? .

Check with your doc. While it sounds like it could be anxiety, it is important to check in with your doctor to rule out an underlying medical condition. To treat the anxiety, your doctor may want to prescribe anxiolytics; however, the long term solution is to treat with psychotherapy & improve self-care. Strategies for reducing anxiety include deep breathing, relaxation techniques, practice of yoga and meditation.
Exercise induced. The mere fact of walking (exercise) will cause your heart to beat faster. Check with your doctor if concerned.
Self-Help Resources. Check in with your doctor to rule out a medical condition. As an additional resource: Free Smart Phone Apps: 1) MyCalmBeat, 2) StressCheck, 3) TacticalBreather,4) LifeArmor, 5) Breathe2Relax, 6) BioZen, 7) BinauralBeats therapy, 8) Instant Heart Rate.