The visible swelling in his neck, the failure to gain weight even when trying, and the major anxiety all point to the possibility of hyperthyroidism, which can be triggered by major life stress such as the loss he's enduring. It probably would not explain the morning congestion, however.
I don't know much about marijuana but always have heard it's supposed to mellow one out, isn't it? Thyroid disease would explain the anxiety more logically, from what I know. He should have his thyroid function tested... Tests for TSH, free T4, free T3, and TSI antibodies.