Had anxiety bp went 160/100 pulse 120 bpm.managed by 2 hrs. then prescribed antihistamine for better sleep but developed boil after 2days.is this bad?

Lots here.: The boil is likely not related to the other symptoms. The insomnia may be related to the anxiety. Yes- that BP & heart rate are elevated. What are you doing to address your anxiety? Talking therapy ranks really high. Cognitive Behavioral therapy or psychotherapy can be effective. Aim for daily exercise, 8 hours of sleep per night & good nutrition w 5 servings of veggies & 4 of fruit per day.

Unrelated: You need better management of your anxiety. Antihistamine other than perhaps hydroxyzine does not offer much help on anxiety . The boil is not related to the use of antihistamine or anxiety per se and may require medical attention if it is getting worse or not improved after a few days.