It really depends on how frequently you feel scared/negative and whether it is only sometimes or "all the time, ie, pervasive sadness. Also you haven't mentioned exactly what scares you? Is it bodily concerns or something else? Grief, after losing a loved one is normal and may lead to sadness. However, depression and anxiety is an altogether different entity and needs treatment. If any of your symptoms lead to socio-occupational problems or are very distressing, please get evaluated by a professional. If on the other hand, the symptoms are fleeting/ occasional, then yoga, relaxation, breathing exercises may help with the anxiety. Psychotherapy, like CBT (Cognitive Behaviour Therapy) may help with negative thoughts (which again you haven't mentioned what they exactly are). If by negative thoughts you mean thoughts of self harm, then you must visit a Psychiatrist asap.