At high doses it is possible for your heart to go into arrythmia - it starts jumping about all over the place. Body temperature can soar, causing overheating. Taking speed with other stimulants like E increases these risks. Amphetamine use can affect sexual behaviour. Male orgasm and ejaculation are inhibited.
Sex can last for a long time.
Make sure that you have plenty of condoms, just in case. Most people who suffer from amphetamine psychosis find that it wears off as the drug does. As they come down, they can distinguish between their delusions and what's really happening. Regular use can cause long-term or even permanent psychological problems. Amphetamines don't cause physical dependence but there is a risk of psychological dependence.