Identify the Synonym for 'Tense'

During a particularly stressful week, David felt quite tense as deadlines loomed over him. He found it hard to concentrate on his tasks. To relieve his stress, he decided to go for a long run in the park. As he ran, he noticed how the fresh air began to relax his mind, making him feel lighter and more at ease after each step.

Based on this context, what is a synonym for tense that fits the situation described?