I don't think anyone can answer this question for you. It's completely situational based on your life outside cards. Here's my example I'll show to you:
I work a retail job and oftentimes have my shifts extended longer, sometimes to doubles. I was asked to leave work one day then do an overnight after working 5 hours already and the overnight was a full shift. Futhermore I have a 1 month old little girl. All of this adds up to little sleep. Just to kick it up one more notch I like to have a few beers every night. I don't go get loaded all the time or anything so don't misread.
All of this is stuff I take into account before I play. I'm not a great player, not even a winning player. At least, however, I try hard to do the good things a good player should do and one of those is not to play tired or intoxicated. When I'm too tired is when I've worked a long day, my daughter is all pissed off and screaming after I get home and I've had a drink or two.
Now that I've told you what it's like for me, you have to look at your life and see what it is for you. When are you feeling exhausted? What's your work like? Is it labor intensive or mentally straining? Do you do a lot of math at work to the point where you come home and don't feel like doing math for the game? Do you have a little kid?
As you see what I'm saying is there's a lot of play in a question so general. I know my limit and I realize you're trying to learn yours. Hopefully you'll be able to look objectively at your life and figure that out for yourself.
My final thoughts are twofold:
When do you sit down to play and think "I'm freaking exhausted, I'll just play a few hands and go to bed" or something of the sort.
The other is a definite answer. Do you ever come to cardschat and see this banner at the top?
Hello Uribam it appears that you have not posted on our forums in several weeks, why not take a few moments to ask a question, help provide a solution or just engage in a conversation with another member in any one of our forums?
If so you've been too tired to play for awhile.
Edit for being too tired to spell think correctly.