Enroute Controller described a loss of separation event listing a number of contributing human factors.

Narrative

A B717 was in front assigned 290+ by previous sector. A Challenger was in trail assigned 290-. I climbed the Challenger to 330 and handed off to Ultra High [Sector]. Ultra High climbed the Challenger and gave aircraft normal speed out of 340. I gave the B717 normal speed and climbed him to 330. At the time the Challenger was above the B717 and climbing. I based my decision on aircraft performance. I thought a B717 normal speed would be 290 or greater and with the Challenger's reduced speed; he would climb faster than the B717. I haven't listened to the tapes yet to see if Challenger checked on 290 or less and I don't know what the B717 'normal' speed was for the day. I was not feeling well that day and decided that I should go vertical with everyone. The Controller at the sector next to me offered his D-Side 3 times and I declined each time. I did not think the B717 would out climb the Challenger and I didn't think the Challenger would catch the B717. I didn't ensure anything. In fact; I took away the insurance that was there. I have no idea why. I am not ever bothered to have help. I have no macho issues. I was aware of my limitations that day and still declined help. I will be totally honest here; I was going to call in sick that day because I had a sore throat and didn't feel sharp. I went to work because it was a holiday; holiday pay. I am so disappointed in myself. I am having issues with medical insurance and as a result I received numerous medical bills that very morning and decided I needed the holiday pay; which I really don't. I am a very safe controller; I couldn't not go to work today; our area has had so many errors recently. I am totally at fault but I still would like to know what the 'normal' indicated was for the B717 yesterday. Also; I want to know if the data block from the Challenger had dropped off my scope. I still feel like I let my area and supervisor down. I am disappointed in my judgment. Use sick leave as appropriate [and] never declined help.